I'd agree with JP!
My dealer offered to do the roof in their approved bodyshop, and said it will still be warantied!
But I chose to get it done myself!

saved money, and it was a better job that the dealers bodyshop would ever turn out!
Resale, it shouldn't affect it, so long as the job has been done well, no blemishs, fisheyes, overspray, or flaking! your car will always be more unique than other ONES!...........(well in it's own way)