From About This Project
Here’s a slick way to keep tools from sliding off the roof! Cut two 12-in. long boards (any width) and hinge them together. Glue a scrap of outdoor carpet to the bottom of one board. Set the boards on the edge of the roof with the hinges toward the peak (the carpeted board will grab onto the coarse shingle surface). Slide a 2x4 scrap between the two boards until the top board is level and fasten the 2x4 in place with drywall screws.