What Can I do and How?

[Hellbent]

If you are going to patch it, make sure you remedy the cause first. I had a similar issue with mine. Turns out the sealant in the rain gutter looked as though it was in good shape; but it really wasn't and in some places was actually bond. You might consider swapping out the roof- as I did.
I found a cab in the salvage- that was on its way to the crusher. Surprisingly, the roof was the only rust free metal on the cab. I cut off midway at the pillars and hauled it home. Measured 100's of times- tack welded angle supports within the cab to minimize twist and cut. Sat the donor in place and welded it off. Did it in a weekend...
Good luck with your project.