A roof skin by itself isn’t any harder to replace than a full floor pan. The only problem is finding the skin. If you’ve got one, it’s not a big deal. And a full floor pan replacement is pretty typical rust in a lot of places. Roof skins replacements just freak people out because they usually show up on cars with more serious rust everywhere else too.
All of these cars cost more to repair and restore than what they’re actually worth. If you’re paying someone else to do the work you can forget ever selling for a profit, unless you hold onto the car long enough for the rising market to create a profit for you. If you do the work yourself and pay attention to costs you might be able to come out a little ahead compared to the cost of parts, but again, you’re not going to make money if you consider labor.
The only real question to ask is if you want to build the car and have the resources (money/time/skills) to do it.