Make one cross-section that's curved right, then you can just extrude that forward as many or as few times as you want to make most of the rest of the roof. Yes, I think that works well when you have a plan for the model, but less well when you have to go back and stitch in new sections. My problem is that I frequently don't know what I don't know, and have to deal with issues when I come across them. I'm sure that will improve in time, though. It's funny, I feel a bit better at modeling people than mechanical things.
Yup, part of spline modeling is "seeing it" before you make it. But backtracking and redoing things occasionally isn't fatal.