I use a simple 2' x 4' box divided into eight sections. Works fine for leghorns, black copper marans, cuckoo marans, production reds and easter eggers. I also don't care if they sleep on top, which is why it is flat.
We have 3 chicken houses, and all have different boxes.
Our big house has 4 14x14x14 boxes with doors that open into the"man room" for easy egg collection. These are the best in my opinion.
Our little house has a black garden center planter about 16" accross turned on it's side. It works well.
Our other house has two communal boxes with collection door facing - yes, you guessed - the man area. The chickens in this house all get along well and 4 or 5 will sometimes be in one box! I think this is ok, but they seem to like to go broody in that house a lot.
Another thought, something to keep in mind: our cohins and silkies do not roost, they like "ground nesting", so if you have non-roosting birds, be sure to give them something to lay in on the floor.