Advice needed on rotted roof

The roof skin isn't any harder than doing the dutchman or corners. In fact it's probably easier than doing the dutchman because the skin doesn't locate anything, the dutchman has to be right or the trunk gap will be off. To replace the whole skin it's just a whole lot of spot welds. About 200 actually. But really it's the same process. Drill out all the spot welds, remove the skin. Fit the new skin, clamp it into place and put all the spot welds back. Sure, there's a lot of them and it will take a lot longer, but the process is exactly the same.

If you do patches you'll have to be a little more careful not to warp the metal, just because the roof skin is a big, mostly flat sheet so it's easy to warp if you build too much heat. The spots you need to replace are fairly small, and being near the edges is a good thing as that will help with the warping vs trying to work further out in the flat panel where there's no reinforcement.