I would use the flanger on roof as well , but i would try the 3m weld-less quarter panel adhesive that way no warp-age. flat sand with 80.
Then use tiger hair filler first and flat sand 80 , then bondo long block sand 80 then 180 and 240 by hand. Then glaze puddy any pin holes. Block again. Use etch primer over bare metal spots light coat.
2k primer 3-4 coats and let it sit in sun (If i had a weak to kill.)
320 block sand again on the long block again and primer again with 2k primer. Then wait one day and block with 400. Clean and prep for paint.
I have done it this way and it takes more time then most like to spend
But i have good results blocking by hand.
This is only if you never done body work some people have there own methods just trying to help .