What are the measurements on the barn tin? It is not hard to put shingles up and surely if you are going to tackle the fast frame kit you can tackle the shingles. If you are going to use the tin I would suggest just making a square building with a sloped roof. It should be fairly easy to do. If you make the front about 6" higher then you put some rafters on an angle from front to back you could lay the tin on top of the rafters. There should be plenty of examples here on BYC. Good Luck!