Designing sets is pretty hard; i'm still learning alot about it. The best way to do it, still, is to do a mockup with foam core or the like, and even to try lighting it a bit. Every time i've used a 2D drawing, its always ended up biting me in the ass; there are awkward or weak angles that don't make themselves apparent in a 2D design.

For this set, i've been doing mockups as I go along; set something up with crude pieces of wood, then take pictures. Move things around, and repeat.

Been using photoshop for the wall designs; i'll take a picture, then draw lines/curves on it, indicating where the beams and pillars go. Works very well, i've found.