rfsystems, we just finished / finalized that very thing ourselves.
In fact, it's coming down to the wire! This is our first year so we had to start from scratch. ZERO wall panels and such. I just got done redesigning my building #2 (part 2 of the haunt, building 3 is maze only) and when I was done, I figured up that I was saving us over $400 in mats and lots of hardwork! I only cutout 2 hallways, that was it believe it or not. Since we're in small (1,000 sq ft) buildings anyways, I figured why waste space on hallways? I still have 1 hallway, but it crucial to our layout / story / setup.
So, also, never hesitate to redo the layout, or to rethink things. I saved a lot of money by doing it this new way and actually, it's going to be easier and I think I'm liking it BETTER than the original.
Allen is right, btw. You'd be totally surprised on how much more sturdy that thing will be with 4 pies on the corners. I've seen 2x2 panels with luan, 3 vert's and I bounced off of it and it was like a BRICK!. Didn't move. I looked at the backsides and it WAS an H, but when I tried to move it, jees.. nah. wasn 't movin! Had one laying on the floor and it felt very solid! much more than I'd figured. So yeah, you have to build smart. When in doubt, SCREW IT SOME MORE! Add pies / triangles, just get to where YOU feel good about it and you're good to go.
Ohh, I also had an impact wall by itself with very little support. This was one of the big fixes I made. Be sure to try and think of everything. Ceiling height, (may have to build wall panels shorter for some reason), impact, lighting, and the "what if's" Just because it's RARE, doesn't mean it WON'T happen.
Looks like you're getting all kinds of help. Post some pics if you can, when you start construction. We likes pics :P