Just chopped the top of my son's 55 F100. After tack welding in the two filler strips to lengthen and widen the roof I noticed the center has now lost it's crown, in fact it is now lower in the middle. Can someone tell me whether I have to shrink or stretch it to bring the center up. Any tips on the best way to re-crown the roof would be appreciated!

 

a good way to do it is find a donor top with good skin, with the same crown.
cut out the old one and weld in the new... good luck