This year 397's robot was quite literally 2 KOP frames stacked on top of each other. We used 80/20 in between them. This made our frame quite heavy but incredibly rigid. It also gave us the benefit of letting us play with the mounting height of our kicker until we liked it by sliding it up and down.
In the past we have used the KOP frame and 1" square tube to build the robot. We bend the tube in house using a standard pipe bender. This can then be bolted together (or welded). The only time this method was a problem was in 2008 when the force of the launcher changed the shape of our frame as we fired. I'm sure someone has a picture of 397 hitting their frame with a hammer to make it go back square. I personally like the bent tube construction method. But as always, you work with the resources you have.
http://www.chiefdelphi.com/media/photos/27139 2007
http://www.chiefdelphi.com/media/photos/23321 2006
http://www.chiefdelphi.com/media/photos/30277 2008
http://farm4.static.flickr.com/3348/...cd2aa38f_b.jpg The fun bent parts in 2009. That PVC ring was a prototype, the final one was made of aluminum round tubing and bent by hand.