you start with 1200 grit paper wet and go finer 1500 than 2000 or 3000(trizact paper) than using a buffer with some(3m) rubbing compound start buffing it out with a(3m) white foam pad than use a(3m) black foam pad with(3m) swirl mark remover and now your almost done just wax the area check for under buffing and swirl marks but be careful sanding too much you don't want to break threw the factory finish one more piece of advice buying all that material to fix your roof can cost some big bucks unless you already own the equiptment and material (buffer,pads,compounds) I would recommend going to a local bodyshop and find the painter and ask him if he could sand and buff the roof out for a small fee $20.00 or less it won't take him long
but that's just my opinion good luck