Hey guys and welcome to my only non in-game guide.
Before you ask, yes this falls into the scope for guides. Since it's game related, sorta.
All the photos are crap because I took them on my phone :/

EDIT: Hey everyone. I have made a group you can join if you want help/advice or just want to show off your mask or mask-like creations.
http://steamproxy.net/groups/themaskmakers
Feel free to join, ask your questions and chat.

The method here is primary school level, sure I have some wicked painting/crafting skills but you learn alot of this in primary school. It's just taking a step further. So be ready to finally put Art class to use.

Still I've made my fair share of masks this way, since it's cheap, but also because it doesn't require any special tools.
As I mentioned everything needed can be found in prison, in one form or another. Plus most items can be subsituted for something else (I'll provide suggestions).

Also the actual masks from the Overkill store are a million times more awesome, so If you have the cash and live where postage is cheap, go for that. But if you live far away and/or want a mask not up for sale, making it is a good option.

Anyway, lets begin.

Base materials:
Newspaper (free if you know someone who still gets the paper or next to nothing to just buy one)
Tissue paper, I used Serviettes (they're a buck a pack) but toilet paper works too, is all the same.
Thin cardboard, I got Cocopops for the box but any thin cardboard works.
Elastic, to attach it to your face. (Note I used different straps, but elastic is more common.)

Optional materials:
Craft Foam (EVA foam)
Pre-made base mask, commonly found at most craft/art shops.

Glues:
Making glue is easy, personally I use watered down PVA glue, (about 2 parts water to one part glue) since it soaks in really well.
But flour glue also works, it's made by combining flour and hot water to make a clear paste. Personally when I do this I use corn flour, since it's stronger.
Basically you combine the flour and hot water (not boiling) to make a paste with the consistancy of jam then combine it with the boiling water and stir until it becomes soupy. At this state it's like napalm so be REALLY careful not to spill it on yourself or others. As it cools it'll thicken more, if it thickens too much just add more boiling water.
It's vegan and safe for kids, since it's just corn but it does go moldy fast but apart from that it's safe to eat and get on fingers. If it goes moldy just throw it out, since it'll get very smelly as well.

Paints:
Personally I use acrylics, the brand I get goes for about $2.50-$5 a tube (depending on the colour).
Any 1/2 decent brand will do tho, some cheap/kids brands don't mix well and can lead to an uneven colour, a big colour change as it dries and so on. But it's up to you what to use.

If you have one, and know how to use it, an airbrush would be excellent, expecially for all those gradients in the mask designs. I don't have an airbrush so that's all I can say on the topic.

Equipment:
Brushes.
Any old brush set will do, but it's good to get all different sizes and shapes. Any art/craft shop sells brush sets and they normally go from about $3-$15 depending on the quality/size of the set.
My brushes are just cheap artist ones so they have a tendancy to drop hairs ( tweezers are good if it happens to you, to pick them out of the paint) just remember to rinse them in water after you use them so they don't get ruined.

Water/paint/glue pots:
You can buy proper ones, they're not that expensive but I'm really cheap.
Disposable plastic cups and plates work and are simple to clean-up afterwards but I went one step cheaper and got ice cream. Where I live you can buy little ice creams in a plastic cup with a plastic lid and they are perfect for water/glue because they seal with the lids and the lids are the right size for paint. During summer they go on sale for about $1 each.

Blades:
This is one of the less "kid-friendly" steps. I use a cheap extracto knife ( that I want to replace) but a box cutter, stanley knife, scalpel, razer blade, etc will work too. You will need to carve out a fair amount of the design and it WILL lead to cuts and scratches so keep the band-aids nearby.
Using a blade is easy. The one rule is: don't cut towards yourself. Basicaly don't put any part of yourself near where you're cutting. The skin is thin on your hands and there are alot of nerves, so it'll bleed and sting like a ♥♥♥♥♥ if you get yourself. (Could be a hospital job if you hit certain spots, even with the pissiest little blade.)

Other:
Balloons.
If you don't have a pre-made mask a balloon can be used to get the mask going or for making any other round shapes.

Superglue.
For attaching various things, like foam. Always test it first, incase there's a chemical reaction with what you put it on. I used some on some fuax fur once and it got so hot it started to smoke.

Staplers, Pushpins, etc.
This is how to put the straps/elastic on your mask. Anything will do really, as long as it'll stay on.

Fine-grain sandpaper
If your mask is too rough, try using sand paper. As fine grain as you can find.

This is why I want to make more Payday masks. It's so easy to get reference pictures with the mask viewer and the Begins version of the heister masks are great, since they're blank.

Here's and example of bad (the halloween teaser) and good (the mask render) reference:
A good reference is:
- a decent size, clear with correct colours
- from a canon source (so from the Overkill site or in-game screenshots)
- the version or varient you want to make

A bad reference is:
- small, pixelated, off colour or blurry
- non-canon sorces like fan art or fan renders
- incorrect details or scaling


The best thing is to get a front and a side picture, but get as many different angles as you can, hense why the mask preview is so great.

The reason you use references is so you don't have to rely on your memory. No matter how great you think your memory is, you will still get details wrong. When making something like this those small details stack up.
Before you say it's a rookie thing to use references, even the pros will have reference sheets on hand.

First off you need to make the basic mask shape. You do this by blowing up a balloon so it's slightly larger than your head. The mask needs to be quite loose, as it'll tighten as you add to it.
Use newspapper, since it's a little more sturdy than tissue paper, to make the basic shape.
Be sure to do a few layers for strengh.
After it dries, pop the balloon and cut out holes for your eyes and nose, also shape the mask into the basic shape you want it.
Scrunch up some newspaper and place it inside your mask to prevent it caving it when you're adding to it.

You should end up with something like this:
That is the base mask I started with, I had to modify them a little since it had a really awkward fit and the nose had a weird Bonnie like point on it. I also cut the exsisting elastic off so I could put mine on later. Also I covered my table in newspaper, it helps keep it from getting glue/paint on it.

Using a combination of newspaper, tissue paper and card board form the details of the design.
Card board is best for the frame for features like the nose, newspaper is best for adding the basic shape and tissue paper is best for fine details. Don't forget nose/mouth holes, air flow is very important.

Use a paintbrush to apply the glue, if you don't want to do it with your fingers, and cover the area well. Personally I have a pot of water and a pot of glue and I use a combination of the two to get the shape right.

Remember to let your layers dry, a friend of mine didn't and the mask went moldy.

When it's dry you can start carving out the fine details, cut a little more than you need because you need to put more tissue over any cuts you make to smooth it out. So you will have a cycle of carving, adding to it and waiting for it to dry again and again. Remember to build from the base mask, not to carve into it. You need about 50mm of mask so it'll keep it's shape and remain sturdy.

My mask took months, on and off (mostly off, waiting for Clover to actually come out), but it'll take as long as you want to put into it. I could of easily poured more time into it but I had to call it somewhere otherwise I'd still be adding to it.
Everyone I showed it to says it looks epic but I can only see my ♥♥♥♥ ups ;-;

Elastic + Staples = simple.

Still I took it a but further and got some straps of an old school bag and used them instead.
It'll take a bit to get the fit right, I have a strap over the top of my head so it won't slide down.
You may need to put some EVA foam in places so it'll sit right on your face. For mine I had to carve out the area around the back of the eyes more so I could fit my glasses in better.
Remember you're probably going to be wearing for a long time. Thrust me, an ill fitting mask is hell.

Also if you're making it for someone else, get them to try it on while you're making it so it'll fit when it's done.

Like I said, if you have an air brush use it. But I don't so this is how I painted mine.
I went for more of a cartoony cell shade over the actual style since I thought it would come up nicer.

First off you start with a base coat. It just makes the surface a smooth even colour/texture for the rest of your colours.
Next is the actual painting. For the eyes and lips I used 3 different shades a base colour, a shadow and a highlight. I was lucky to have a paint labled "Light Green' that was perfect for the shamrocks.

Painting takes very little time to do, but a while to get good at. I'm probably not the best person to explain techniques, etc but just experiment. You can always just paint over it and start again.

Still grab your references tho, the human eye can be very weird when it comes to colours and matching them. What's green to one person can be blue to another.

Again with brushes, experiment. I can't talk for anyone but myself, since everyone has different brushes and ways of using them.

Paints on the otherhand. Everywhere gets different brands of different qualities and colours. No two brands have the exact same red labeled as red. I have about 3 different brands in my set. I have a shopping bag with about $60 worth of various tubes of acrylics. Still it's up to you what you buy and use.

My phone was very nice to take only the ♥♥♥♥♥♥♥♥ photos possible, still that's it done right after I covered it in more PVA glue to seal it. As well as a picture of a certain other mask I made.
Still it's alot of fun to make and it's cheap and easy if you want your very own heister mask.

Be sure to link me any of your own, I'd love to see them. Still it's not hard to make, it just takes a bit of time and effort. This method is about as "kid friendly" as you can get. I'm probably going to make a few more (my friends will shake me down for some) so I'll probably add more pictures in the future.

Also I've been asked ALOT of questions since posting this guide so here's a FAQ:

Q: Can this be used to make x or y?
This method can be used to make any mask or small prop you can imagine. All you need is the skill and time to make it.

Q: Why is corn flour better than normal flour for making glue?
I'll explain it the least chemistry filled and shortist way possible. Basically corn flour and cold water make a non newtonian fluid, like custard, it bonds to the paper fibres better as it dries. Thining it with boiling water keeps it a liquid so it can soak in. Sure it's thinned/watered down but it's still very strong, since it's absorbed into the paper it makes the paper mashe stronger.

Q: Can you make x mask next?
Sorry but no. Like alot of people I have an actual job that takes up a fair amount of my time. I normally have something I'm working on too. In this case it is a Wolf mask, but I have no ETA on that.
Also I don't do requests for physical props and I only do paid commisions for people I know IRL.

Q: Will you add more/better pictures?
In due time, when I get around to it. Currently I'm getting ready for a convention, so it'll probably be after that. Still I'll try my best to keep updating this guide.

Q: I wear glasses, will this still work?
I also wear glasses and it fits ok for me, since the mask rests on top of my head. Still you need to use your blade and make room for your glasses inside the mask.

Q: You spelt x word wrong.
Two reasons, first try typing/editing guides at 2am and being able to type good. Second, I'm Australian so I use Australian english. Meaning it may have different spellings from US english.

Q: Can I wear this in public?
A: Not sure. You have to check local laws about the wearing of masks in pubic and so on.
Just remember if a cop or guard tells you to take it off, you probably should.