OFW,
I think Tim is talking about rolling Beams, Channels, and Angles rather than ga. sheet metal. It takes some pretty hefty equipment to roll those items to a consistant radius.
Tim,
Figure on square or rectangular tubing to wiegh more when you get it back than when you sent it. They will put "S" shapes(I beams) plus plate shims inside the tubing to keep the tubing from crushing under the rollers.
Just something else to think about,
John Wright