Actually looking at the overhead projection again he must have taken an orthographic shot of the floors and then taken a bunch of different shots of the walls and stitched them together in Photoshop. Which kinda seems like the hard way to do it.... Or... Perhaps he had two different models, the main one which he could take the iso shots with, and then another for the top down shot where he scaled in (or out considering he probably did it room by room) the upper parts all over the place on the horizontal plane (which I think is how I would do it).