Today's progress on my game engine hasn't ticked off any feature boxes but it has added sufficient backend extras that I can handle all the properties for the map tiles in memory and begin putting together a world edit tool.
So right now the map can store if its solid, and what the ceiling/floor height is. It can also store the slope of the ground /ceiling and separate textures for all the different parts of it. What it can't do yet is use that data in the rendering.
Yes it looks bad right now but I'm trying to take a (torn) leaf out of @TodePond 's book and share some scrappy fiddles.