Concrete
What I have is not a chicken coop but a large old dairy cattle farm, I raise goats now. The barn is too open by its self but my father and I have constructed a veeery large chicken "cage" on the concrete floor I use a deep litter system which is keeping them on wood shavings (I have a free supply - benefit of being a wood worker) but instead of changing it all the time just move it around and put new litter on top of the old one. In the winter it provides heat, and by the time its summer it has developed antibacterial qualities. Before it starts to get cold i shovel it all out hose down the floor and start it all over again. This is something I learned from my grandmother who was a sheep farmer (Eugh sheep got rid of them) since then I have researched it extensively and if done correctly it is perfectly fine. One must however turn the bottom layers up in order to allow it to breath instead of fermenting and new litter must be added on top of old soiled litter. would not recommend this method to anyone with linoleum or wood floors, concrete however is ideal for this seeing as this method can counter act concretes heat-leaching tendencies in the winter time. I am not sure but perhaps you could pour some concrete over your existing floor?
