Maybe this old thread will give some pointers.

I guess it depends on how much height you need to. When I said I didn't do 3d iso, well I had stairs and columns you could want behind/under and stuff and I didn't need any special tricks AFAIR. I just drew everything in the correct depth order I think. I made a winforms isometric map editor, the artists did the rest so all the map editor did I think was place a any-shaped tile at the tile position. The artists knew how to draw the tiles like that. I lost everything to do with that game almost except the codebase that went onto become a different game. It was a really cool mixture of different perspectives and stuff that was really charming.