You can use slate or ceramic but I used porcelain tile on mine. It is glazed but textured so they have no problems running around on it. I was going to use slate but slate can absorb stuff and it just seemed better to go with porcelain for me. You can cover as much of the bottom as you want with tile and then cover the rest with something else. For Emerson's tank I have it all tile and then used a smaller tile raised up for his basking area/warm hide. He seems to prefer it, I tried changing it to slate rocks and he wouldn't use it, lol.
