Need Help with Vinyl Roof Disease on '72 Scamp

First, welcome from Fredericksburg, VA.

You essentially have three options:

1. Scrap the car and find a better body. That is probably the most common recommendation you will get with that kind of rust.
2. Find a good donor where you can strip a solid roof skin and just do a roof skin swap. You can do this yourself if you have someone who is generally knowledgeable about body/sheet metal work or if you are.
3. Do something radical like this: They Said It Can't Be Done...Or Don't Even Try.

My Dart roof was in about as bad a shape as yours. I just happened to get lucky and find a perfect donor car. I was also working with an experienced body man, so we tried this radical nonsense together. In the end, it worked. But I also reinforced the subframe because of the complicated body work that we did. As bad as that roof and rear section is, you have to just consider diving in if you don't want to really scrap it. Worse case, it is just time and money.