Remove any loose or jagged debris from the roof. For instance, if wind has lifted or curled metal roofing panels, either remove the damaged panels or trim them.
Anchor one end of the shrink wrap under a 2-by-4 nailed to the roof edge. Attach the 2-by-4 to the roof with nails.
Stretch the shrink wrap over the damaged section of the roof. Secure the other end and the sides with more 2-by-4s nailed to the solid portion of the roof. Extend the shrink wrap at least 8 inches beyond the damaged section of the roof on all sides. Cut the shrink wrap with the razor knife.
Turn on the heat tool. Starting at one edge of the shrink wrap, press the trigger on the heat tool and sweep it slowly from side to side, holding it a few inches above the shrink wrap. The wrap will warm and begin to tighten. Move in a slow, even rhythm up and across the shrink wrap, until all the wrap has been heated and tightened.
Check for holes or tears in the shrink wrap. Apply shrink wrap tape over any holes or tears to seal them.