Surely for stairs you can just use the bsp collision commands to let your player walk up them. Providing the player is positioned in a sensible place to start with it will work fine (i.e. place them on the map not stuck in a wall or something). Then use the camera to object tracking commands to let it slide smoothly around walls, etc.
Doesn't help with object placement too much (you still need to know the right height, etc) but definitely helps with stairs.
Cheers,
Rich
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DB Team / Atari ST / DarkForge / Retro Gaming