help straighten my tin can toyota roof!!!

well i got a 1993 toy, and the roof is like a tin can. no braces at all on the roof. i guess it got warped, so theres a lot of tin can action. in class today we heat shrinked it, but it would just move to another spot. anything to help? trying to use as a little body filler as possible. any ideas to get rid of it (besides ragtop lol)

get a nother doner roof and chop the top. good luck