The metal shaping forums have lots of info on how to put a crown in a flat sheet. try metalmeet, metalshapers assocation. and there are a few other metal forming sites , I took a class at UVU, street rod panel fabrication, and a weekend with Ron Covell, David Gardiner in the uk has some good info on his website, and sells DVD's working with simple hand tools. http://www.metalshapingzone.com
It's easy to put too much crown in a panel, then have to bring it back . Here on Hotrodders, Cboy has written an eBook, "the scratch built hot rod," click at the top of the page. When I go south for the winter I plan on building new doors for the 29 Nash roadster. an amazing build is Chris Davenport's 40 willys, all aluminum body he built as a student at UVU.. Google "Chris Davenport 40 willys"