At the beggining of the game, we have to place two essential buildings: the granary and the market. We should take care to place these on each side of the keep so when attacked only one of them gets demolished. Following Rat's methods we should only build one stockpile.
We should place the granary near the stockpile, then separate it with walls from the rest of the castle, to which there should be only one entrance. Then we place the armory here, a few blocks apart.

Next up we place three wood cutters close to the trees then five apple orchards, these should be more than enough to sustain the peasants, coming from exactly two houses.
We need only one quarry with two ox tether.
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We place the barracks to the furtherst side from the enemy. We need only 4 or 5 workshop. Spear and bow production should have the ratio of 2:2. We can do this in 2:3 but in this case bows should be the 3 because its made slower. Another viable strategy is to have 4 or 5 bow producers and we buy the spears off the market.

Since the granary and armory are enclosed and thers only one way in, we should next enclose the keep itself with walls and place a gate in front of the campfire. Everything else will be outside the castle. The barracks and market needs to be fortified further with walls to protect them from catapult fire. The mines dont need any walls arond them and houses should be also outside the castle, the workshops can be fortified as needed.


The best thing about building like Rat is that we can completely ignore symmetry and some outgrows in the castle but we can also place separate non connecting walls as we like, truly capturing the aesthetics of a Rat castle.
Behold the end result:


All we have to do now is to spam archers and spearmen to our heart's content and be like a real Rat.

• Theres an istance of Rat not building a gate at all and we use stairs to move in/out.
  
• In some instances the granary opens to outside of the castle, but sometimes its separately enclosed and stairs are used to move around.
  
• Sometimes Rat builds a small tower at a random place which we should emulate but only one such tower should be placed.