We had a dirt floor until this summer when we topped it off with several inches of sand. Rented a trencher when we constructed the coop 7+ years ago - dug out narrow trenches about 1 ft deep and put pressure-treated plywood down, then backfilled with dirt and built up from that. The plywood is still there doing its job. Added sand this year because the dirt floor level had gradually fallen and did not drain well. In the winter (dry season here) I used to add pine shavings on top of the dirt, but not in the wet summers. Our coop has open sides all around - only chicken wire over wood framing, no solid walls, to allow good ventilation, but lots of rain blows in. I don't think I would change anything about the floor in my environment.