Before you glue up wood for a project, examine the parts. If at all possible, start out with cleanly cut, perfectly straight boards of the proper thickness. Take out any bow or warp before you begin your gluing work. By using straight and true stock, you won't have to force the boards in one direction or another, and you won't have to get into tricky, complicated clamping set-ups.
If you are replacing your old, worn out roof covering with new asphalt shingles, make sure they have a Class 4 rating under Underwriters Laboratories’ (UL) 2218 standard. A Class 4 rating tells you a sample of the product did not crack when hit twice in the same area by a two-inch steel ball.