I use pine shavings. They are readily available at just about every farm supply and feed store, and the price isn't bad. They give off a nice fragrance of fresh pine and all in all look good. Hay is my second choice, as it is a good insulator and heat absorber in the winter months, however I use hay in the nesting boxes, so I try not to put it on the floor all the time so the girls don't get the wrong idea. I would not leave a coop floor as dirt for parasitic reasons, as well as the compaction and "caking" that will result from chicken waste constantly being walked on on a dirt floor. There isn't really a way to clean dirt. Another idea (which I often imply in my enclosed run) that is a money saver is grass clippings. Although this only works during the spring/summer, it provides a nice base layer and doesn't cost a thing. I put fresh grass clippings into the run right after I cut my backyard. The birds love digging around and finding bugs or other treats that have been chopped up like dandelions and weeds. Fallen leaves are also an idea for the fall, however leaves aren't available in all climates (but there are an abundance here in the Northeast!!). There isn't really a wrong flooring, and you can switch things up as you wish, but all the things listed above are the main things I use.