You were wise to add a photo, I’ve never been help to anyone from a description of a problem. It’s even hard for me to comment without running my hand over the panel to feel what’s going on.
I would get some sheet steel strips sheared (16 or 18 gauge, 1” to 1 ½” wide) and lay them on the roof after you’ve crowned them a bit. With a bit of tweaking you should be able get the crowned strip to lay on the roof where it flows and looks correct to your eyes. You might have to move the car outside to get a more distant perspective. When that strip looks like it flows correctly with the roof skin it will show you right away where your low spots are. Some lows may be able to be bumped up with an appropriate dolly with some weight to it. Where you’ve welded will likely need on dolly hammering to stretch out the shrinkage and correct the panel flow. Progress should be constantly checked with the steel strips. I’ve had problems trusting wood roof ribs as a guide, they just weren’t accurate to be a guide for a flowing steel roof IMO. Good luck, this job may take some time
. ~ John Buchtenkirch