I still use Hardpoints' ceilings from A Dungeons and Dragons for the crypts and some other tilesets chico didn't touch. Despite being mirrored tiles, I find some to be more logical than simple, domed ceilings. The Sewers' roof even gives a sort of claustrophobic vibe. You can mix and try several different styles for each tileset, since they can even be "divided" into smaller sub-sets, like the city interior and exterior, rural, etc. It makes them more varied.