I have old wooden crates that I put under their roost. I lined the bottom with cardboard, put in a couple of inches of straw. When the smell starts, I add another inch or two of straw. When the crate is full, I take it out and dump it in the compost pile and start again. It has helped keep the smell down, makes for a very hot compost pile, and it is very easy to clean as all the droppings are contained in the crate. In my secondary coop, I used an old army ammo box, the handles make it so much easier to carry and dump.