You don't necissarily have to re-base if your careful, thoughit is very hard not to rub through when feathering the clear coat out.
I used 800 and had to be VERY careful not to rub through as the exposed base had been so for a few years and was badly oxidised.
The roof on the car I did now looks better than the rest of the car lol.
If it has freshly peeled, use 600 and lots of water to feather out the clear, just be very careful not to rub through the base colour. then you need to mask with a soft edge about 10 inches down the pillars and right on the roof mouldings. Then you will need to rough the surrounding good clear with white (white in colour) automotive scotch upto your masking. That is so any new clear upto the masking wont peel again. once dry and masking is removed you can use a cuting polish to blend it. That will remove the scatching (tooth) that you had made with the scotch.
Haha I'm not good and explaining things but hope that helps.
Don't forget to clean just before you paint with prepsol, or something similar.