I'm using dirt. Here is what I did. Concrete floor, then tar paper for water barrier, then tarp that runs up the sides about 12 inches. I used screws to hook the tarp eyes over to hold the tarp up. Then poured dirt on to the floor. As the girls poop, I add more dirt, up to about 6 - 8 inches. Then, I pull the dirt out and "voila" Compost. Put the dirt into your garden, and replace it with dirt that needs fertilizer. We have four garden boxes that will be rotating through to be fertilized.
I have heard of the sand idea. Thought about that one. But, since I already have the dirt, ad don't need/want to buy sand.....
I put 6 inches of sand on top of dirt in my run last summer after the grass was gone. We had to go over the sand this spring with a rototiller to make it soft again so it would drain. The chickens had packed down the sand so it drained slow after a rain. Now its great again and chickens are enjoying dust baths and scratching again.
I live in sand and I must say I love it! The rain is drained with-in 5 minutes and a plus the sand dries the poop and lowers the smell! I have a pen that we used to have a garden in that is imported dirt. I smells bad if I don't get it clean!