My enclosure is about 12 x 16. I have a little store bought chicken house along the back wall. I used landscape garden stones and made a sand pit in the corner. It comes out from the corner about 4 ft and then across (like a large triangle) My chickens love it when I rake it and get the sand all loose for them. I made two more smaller ones under the little chicken house. In the summer all of them find their favorite spot and almost bury themselves in the loose sand. I have decomposed granite on the floor of the rest of the coop. It drains so good. Only part of it is covered. The sand areas are covered. Before we covered part of it the large sand had full morning sun. The chickens loved it. I did not cover the entire coop with sand because I walk around in it a lot and the sand was all over my shoes. I can use my ipad and insert a picture if you want to see it. It's raining here right now so I'm not sure how good it will look.
I would love to see a picture if you can upload it