My original chicken coop was a small building built out of scrap lumber, it had a dirt floor. and I'll tell you I'd never do that again! Not only is it impossible to really get clean but it makes for easy rodent entry. After a few years with that we decided to convert one of our unused pig sheds into a chicken house. This building has a concrete floor, as was used to house pig originally. Generally I like to put a layer of hay on top of the concrete, which has worked out well, and my guinea keets, and ducks like to use it to nest in. The really nice thing about it is it's easy to clean up when it's time. Fork out the dirty hay and if needed hose it down. We are talking about adding on to the coop. If we do that the new portion would probably have a slightly raised wood floor.