Hi Zola, I put down cement board (like hardibacker that is used for tiling) as the base for my coop, then flopped the coop right on it (the weight keeps it down). No worries about anyone digging in and it never gets moist even here in the NW! I think cement board would make a great floor, you could screw it down. It is easy to clean, but you could put vinyl on top if you wanted. Just make sure you have a fairly sturdy floor, good joist spacing.
