I’m curious about this as well. I put chicken wire on my coop floor but it’s impossible to clean out because the rake always gets stuck and it eventually rusted holes in it because of the waterer being in there. Then I tried pine shavings and that was super messy and dusty. I currently have coastal hay down and that seems to be working ok and is easier to clean since the wire is gone but I always have a fear of something digging under and getting in. We live in Austin in the city but I’ve trapped numerous possums and one raccoon.
I wondered about using pallets and filling in the gaps with extra boards and setting the coop on that then using hay on top. I’m not sure about sand though but I’ve seen people do that.