It's OK, I think I understand. When you go to place a roof piece, at one point in stretching it across the room it will jump and face in another direction. Is that right?
Some of the roof pieces (like the triangular gable roofs) have a long version and a short version, so if the first one doesn't orientate correctly the second one probably will. For others, like the half-roof pieces, try starting from different corners and seeing how they come out. If that doesn't work, I'm afraid there isn't much else you can do apart from reconsidering your design, in my experiemce.