I also used hay at first....when its new its soft and clean...etc...once they start to poop and all it becomes yucky, clumped up...sticking together in one large lum..etc...and stinks....I switched completely...I also found out that Hay is HOT in summer...and I wanted to keep my babies cool. and I was having to replace and clean it almost every day!!!! AND OMG!! THE FLIES THAT WERE SWARMING!!!!
So I got shavings instead, covered all the bottom of the inside of the coop, and it was nice!!!! I put it in about 1mo ago...I havent had to replace it or clean it out much!!!! Its great....I go in, as I talk to my girls...I get the rake and I move it around....when I do this, I throw in also a small amount of feed, this teaches them to move the shavings around themselves and help keep it clean....Its made such a difference!!!! No flies at all!!! which I love, I also put it in there nest boxes..its soft on there feet also.
On the outside, which is there run, I went and bought a truck of sand...18 bucks for a large size truck of sand, I covered the entire run, including under the coop....they love dust baths, and they dig holes when its hot and make cool spots...every few days I go in with a hoe and I turn the dirt over, man they run like crazy looking for bugs, and playing!!! I do this to keep the dirt nice and pretty...push the poop down into the ground, then it looks like when I just put it down. Ive had it like this over 1mo I think and ITS WONDERFUL!!!! when you wet the sand with a mister...it makes it alot cooler for them also.
As you can see, I have it all on the floor....they roost over all the top of the coop....I havent had to change out my litter in over 1mo.