I had mine replaced and it fit really good from what the body man said. I will tell you to check your window moldings BEFORE you weld in the panel. The rear top corners aren't stamped the best and most of the time leave a gap b/t your molding and the radius of the roof skin in the window channel.
Check out the forum body shop section at
www.camaros.net and do a search on roof skin replacement. You'll find plenty of information on it.