One time when I rolled my 'S' I fitted a new roof panel in one day. Just cut the old rof off with an air chisel, clean back, leaving the original roof flange in place, then weld a new roof panel in place onto the original roof panel flange. The flange ends up very slightly thicker, but it makes it a 'proper' job and there can be no problem with distortion. By the time you b****r about trying to joggle a filler piece, weld it in with a continuous fillet weld, grind back and then have to use filler, followed by a lot of high-build primer and sanding back to the correct profile, you might as well just put a new roof panel on.