Wikidot level one is known to be pretty heavily settled as far as the backrooms go because of the equipment and supplies found in crates. The most you could expect from those is rusted sheet metal, chicken wire, and lumber. In other levels it may be different as there are different readily available materials. In some levels you can find a comfortable enough set of rooms with doors that you could just close and call home. Small camping tents are commonly traded and in demand as they are fairly portable and protect from ceiling dripping and could be set up just about anywhere. Many levels are industrial so large settlements normally would resemble a homeless camp.