To be fair, I've only owned one house to date, and thankfully it was neither a disaster waiting to happen, nor in a hurricane zone.
Instinctively, I'd say that other than making sure the wiring is OK (might have fried a circuit or two if the thing was struck by lightning, rewire as required), is the roof. You may end up finding that the whole thing doesn't make it much longer and needs replaced, and at that point I'd guess you're looking at 5 figures and a likely equity loan to solve the problem. Which isn't the end of the world, but it could hurt if you're dropping below 20% equity in the house.
Oh, make sure there aren't a ton of shingles underneath the top layer. One place I looked at had 3 roofs on it, and they ALL needed to go.