It's kinda funny, But my brother and I had a couple bonding sessions for a few months this past winter and ended up with something very similar to what you posted in the first post.
We used 3/4" round conduit for the whole thing. I oppted for pipe bending instead of welding the corners. The conduit is so thin that it just crompied, so I position some 1/2" rebar inside the conduit at the corners and used the pipe bender to get my 90s. I also used the 3/4" for the base crossbeams and the vertical supports. We made 4 "U" shaped peices out of 4 10' pipes then welded 2 together to form 2 squares. then welded the 2 squares to 5" vertical supports to hold it all together.
We didn't encorporate a lightbar at the time, but I want lights now. I think (if it's ok with you) that I am going to modify it a bit so that the top "sqaure" stops about 1' shorter than it is now but leave the bottom square it's full length. The rack I made is huge. it starts directly above the back window and comes to about 6" from the front of the roof.
One thing I did do different that I like over your design were my mounts. Instead of welding the mounting plates directly to the rack like you did, I made then detachable. I used steel bar to make the bolt plate and used more 1/2" rebar to make "pins" welded to the plate. I welded 3/4" "sleeves" into the bottom of the rack. That way, the sleeves slide down over the permanent pins. I drilled a small hole through the pin/sleeve assembly to instal some small cotter pins. Everything is nice and snug, the cotter pins hold it all in place, but can be removed so that the rack can be lifted off. I figured it would be good to have it easily removable.
I have some Qs for ya, silly stuff that I noticed when making mine...
1) Did you notice that the front mount points site about 3" wider than the back ones? I made my rack completely square. When I sat it on the roof to tac measure the mounts, the front sat inside them instead of on them, but the back was perfet. I got all pissed and figured I had not made it square, so we spun it 180. The back still sat perfect and the front was still in about 3". I just made a wider bolt plate for the front and everything worked.
2) Did you have any issue with the stock "bolt sleeve"? Where the stock rails screws going into the roof, there is a little brass sleeve that they screw into. Like 3 of mine spin freely after taking out the stock screews. I had to do a tittle tiny tac weld on them all to hold them in place so I could rescrew stuff. Did you experience that at all?
I'll post some pictures when I get home to my digital. I would have posted sooner, but I'm trying to avoid blowing $1000s by seeing all the neat ideas on the boards, so I try to avoid them