Thoughts on how to fix a depression in the roof
If the panel isn't full of bondo a good old school body man may be able to shrink the metal alternating hot and cold. Seen it done with torch and water, sometimes dry ice. Final touches done with a shrinking hammer and dolly.
There is another alternative that is a butcher way of doing things, but if you don't have the budget for a roof skin replacement, you may be able to pull the headliner and glue some 1/4 plywood on the underside of the roof for support to keep it from oil canning again.
Wish you luck sir.