Generating the layout of a map for DOOM is easy since the maps are essentially just 2-D structures composed of convex polygons with variable heights thrown in a

Generating the layout of a map for DOOM is easy since the maps are essentially just 2-D structures composed of convex polygons with variable heights thrown in at the polygon level (aka sector). I'd imagine everything but the 2D geometry of the scanned area is randomly generated (textures, item and monster placement, heights of sectors, light levels, etc).