1. On Wednesday you buy everything listed, except for 2 cases, you buy those when 2 slots are freed from the delivery area (since it can only hold 8 and you need 10). You can buy them in advance too and put them in storage. If you don't have enough money to buy everything (53k-ish), you need to buy less of each part and build fewer of the PCs.
2. You assemble the PCs according to the instructions.
3. You put the completed PCs into the cupboard.
4. You advance to Thursday. You'll get Rigg's offers in the mail, accept them all.
5. ????
6. Profit.

That's the gist of it, I'll explain how it all works in the last section ('Mechanics and explanations').

Build:
10x AMD Ryzen 9 Sixteen Core 5950X
10x Mortoni Thermal 100
10x GIGABYTE B450 AORUS M
20x ADATA XPG GAMMIX D10 4 GB 2666 MHz
20x ASUS ROG Strix GeForce RTX 3090 O24G
10x GIGABYTE M.2 PCIe SSD 128GB
10x CORSAIR HX1000
8x + 2x Raijintek PAEAN M

Assembly instructions:
Make sure to install the OS. No other installation/setting needed.

Spooky maths:
3DMark Score: 26665 (you don't need to install nor run it though)
Rigg's offer: 13400
Cost of PC: 5025
Total profit per PC: 8375
Total profit per week with 10 PCs: 83750

Video:

Build:
10x AMD Ryzen 9 Sixteen Core 5950X
10x Mortoni Thermal 100
10x MSI X570-A PRO
20x Patriot Viper Steel Series 4 GB 3200 MHz
20x ASUS ROG Strix GeForce RTX 3090 O24G
10x GIGABYTE M.2 PCIe SSD 128GB
10x CORSAIR HX1000
8x + 2x SilverStone PS14 (Black + Window)

Assembly instructions:
Make sure to install the OS. No other installation/setting needed.

Spooky maths:
3DMark Score: 27242 (you don't need to install nor run it though)
Rigg's offer: 13700
Cost of PC: 5040
Total profit per PC: 8660
Total profit per week with 10 PCs: 86600

Build:
10x AMD Ryzen 9 Sixteen Core 5950X
10x Mortoni Thermal 100
10x MSI B450M Mortar Max
20x CORSAIR Dominator Platinum 4 GB 4000 MHz
20x ASUS ROG Strix GeForce RTX 3090 O24G
10x GIGABYTE M.2 PCIe SSD 128GB
10x CORSAIR HX1000
8x + 2x Raijintek PAEAN M

Assembly instructions:
Turn on XMP in the BIOS (in the 'RAM OC' section, then in the 'Settings' section press 'Apply changes and restart'). Make sure to install the OS.

Spooky maths:
3DMark Score: 28008 (you don't need to install nor run it though)
Rigg's offer: 14100
Cost of PC: 5210
Total profit per PC: 8890
Total profit per week with 10 PCs: 88900

Build:
10x AMD Ryzen 9 Sixteen Core 5950X
10x Mortoni Thermal 100
10x MSI X570-A PRO
20x CORSAIR Dominator Platinum 4 GB 4000 MHz
20x ASUS ROG Strix GeForce RTX 3090 O24G
10x GIGABYTE M.2 PCIe SSD 128GB
10x CORSAIR HX1000
8x + 2x SilverStone PS14 (Black + Window)

Assembly instructions:
Turn on XMP in the BIOS (in the 'RAM OC' section, then in the 'Settings' section press 'Apply changes and restart'). Make sure to install the OS.

Spooky maths:
3DMark Score: 28008 (you don't need to install nor run it though)
Rigg's offer: 14100
Cost of PC: 5080
Total profit per PC: 9020
Total profit per week with 10 PCs: 90200

Note: if you have OCD and can't live without nice round numbers, use Kingston A2000 NVMe PCIe SSD 250GB as M.2 drives instead of the GIGABYTE ones, this should make your profit per PC exactly 9000. Honestly, I like it over 9000 XD

Build:
10x AMD Ryzen 9 Sixteen Core 5950X
10x Mortoni Thermal 100
10x MSI X570-A PRO
20x CORSAIR Dominator Platinum 4 GB 4000 MHz
20x ASUS ROG Strix GeForce RTX 3090 O24G
10x GIGABYTE M.2 PCIe SSD 128GB
10x CORSAIR HX1000
8x + 2x Open Benchtable OBT-BC1 (Silver)

Assembly instructions:
Turn on XMP in the BIOS (in the 'RAM OC' section, then in the 'Settings' section press 'Apply changes and restart'). Install the OS, then install GPU Tuner (and restart to have it installed). In the GPU Tuner app set the voltage to maximum (+50%), the Memory Clock (bottom slider) to 2100 and the Core Clock (middle slider) to anywhere between 1953 and 1963 (these values also work). Make sure to hit Apply in the app.

Spooky maths:
3DMark Score: 35835 (you don't need to install nor run it though)
Rigg's offer: 18000
Cost of PC: 5229
Total profit per PC: 12771
Total profit per week with 10 PCs: 127710

Note: this build is based on spelljammer's build from his guide. It is optimized a bit, but it can still be improved upon (GPU and PSU), but by the time I realized how, I already made the video, so this is all you're getting :)

Video:

About Rigg's Rigs:
Rigg's Rigs is a game mechanic introduced and available only in the IT Expansion. It replaces the base Career mode's PCBay with a broken powerful moneymaking option, that can make the grind for money completely become a thing of the past. The way it works:
-It unlocks on the day after you've hit level 5
-It has a special cupboard in the first workshop, an office space to the left of the entrance in the second, and some floor space on top of the stairs in the third. This is where you have to put the PCs you want to sell. You can put them in on any day, except for Thursday. There are only 10 slots in them, so that's the maximum amount of PCs you can sell per week. If you change workshops, the PC in there goes with you (so you can't have 30 slots, only 10 total).
-Every Thursday when you had some PCs in Rigg's space, you'll get an offer for those PCs from Rigg, in your email, in a separate email for each PC. It lists the parts in it, its cost, Rigg's offer and your profit, should you accept the offer. The word "offer" can be misleading, however, since there's no such thing as a counter-offer, for the same PC it is always the same: half its 3DMark score, rounded up to the nearest 100. For example, a PC with 30001 to 30200 score would get an offer of 15100. You either accept this offer, making the PC vanish and getting the money offered, or reject it, and nothing happens, the PC stays there, you can either take it out or leave it there for next week (but you'll get the same offer, so no use doing so).
-Your profit per PC is Rigg's offer minus the PC's value (added value of all parts in it).
-The only requirement for the PC put in the cupboard for sale is to have it in a 'Ready to boot' or 'No operating system' state (meaning everything properly installed, cabled, etc., only OS not installed). You don't even NEED to install the OS, but you WANT to, since if you don't, Rigg will penalize you by reducing the offer by 10%. 3DMark doesn't have to be installed or ran, this incurs no penalty.
-In case you use used parts, their value shown on the PC will be lower, meaning your profits will be higher. This is the main reason why Tim's Bargain Basement exists (although I still think it's useless).
-Unlike with PCBay, you can only sell fully completed PCs, but you can use brand new parts too (and I in fact recommend it, since Tim's BB is garbage), since the offer is based on 3DMark, not the value.

About the builds:
The builds in this guide are tailored for individual playstyle preferences, and are ordered from lowest profit (but fastest) to highest profit (but slowest). The part lists are in order of the shop's categories from top to bottom. Please make sure to buy only 8 cases at a time, you can put 2 in storage or build them, and order the last 2 afterwards. Alternatively, you can pre-buy the cases (and the parts too, although not recommended due to the newest parts being in the bottom, making them easier to find) during the week.
We don't do CPU OC as it would take too much time with all the clicking needed and it also doesn't give us as much of an advantage as OCing the GPU, while taking up precious thermal capacity. If anything, you'd probably want to underclock it. We also don't use watercooling, since it's too much of a hassle to build the loop and fill it 10x.
When you're first given the option to sell via Rigg's Rigs, you probably don't have enough money to build 10 of these builds, so just build less of them. Don't be afraid to go into negative bankroll, since you'll earn it back instantly on the next day (you can have a maximum of 3000 in debt).
The explanations for the parts used:
CPU: always AMD Ryzen 9 Sixteen Core 5950X - best base score without OC, compared to its price
CPU cooler: always Mortoni Thermal 100 - since we don't do CPU OC, we just go with the cheapest option
Power supply: always CORSAIR HX1000 - you could alternatively use the EVGA SuperNOVA 1050 GS, it changes nothing. 750-ish wattage would be enough, but these are the cheapest PSUs that have at least 6 pins to connect our GPU.
Drive: always GIGABYTE M.2 PCIe SSD 128GB - this can be literally anything, if you put in a cheaper drive you can save 10-20 pcbucks per PC, which in my opinion, is not worth it, for how slow they are. This is the absolute minimum speed you need to not go completely bonkers while waiting for it to install/boot. On the speedier side, if you're willing to give up 20 pcbucks of profit per PC, the Kingston A2000 NVMe PCIe SSD 250GB is a powerful alternative, that installs/boots way faster. Anything more expensive than this is a waste of profits, however.
GPU: always ASUS ROG Strix GeForce RTX 3090 O24G. With the recent changes in 1.13, base scores vary greatly between the same type (3090) of GPUs, and most Nvidia cards are even powerful than before, so you need the best base score to price ratio, like with the CPU. For the OC build it's not the best, as explained in the notes there, but still very powerful.
Case: for speed builds I went with the Raijintek PAEAN M, since it shaves down a few seconds per PC due to not having PCI covers and only needing to remove the front panel and PSU shroud, and not even having to put back the shroud at the end. For profit builds it's the SilverStone PS14 (Black + Window), which is the cheapest case. For the OC build, since we're not using watercooling, the Open Benchtable OBT-BC1 (Silver) is the best possible option, with a 0.7 cooling multiplier (not a direct multiplier, and I won't go into the details, just know that the benches have 0.7, and Paean, Paean M and Enyo cases have 0.5). The silver variant is 10 bucks cheaper than the other two. It boosts our GPU OC even without any fans, so it's perfect.
Motherboard and RAM: I won't list them. The consideration is that the motherboard governs the frequency of the RAM, with or without XMP (without XMP the CPU would be a factor too, but the 5950x has a base frequency that's high enough for this not to matter). So the consideration was always getting the right RAM frequency with the right motherboard. With the Paean M it was also important that it actually fits in the case (Micro-ATX). They also have to be SLI-compatible for the dual-GPU setup. So the ones in the guide are the combinations that yield the best results, with regards to performance and price.

Special thanks:
PUC_Snakeman
spfnym
spelljammer
Without you guys' guides and tools this guide (nor my other ones) couldn't have been completed.