Remove any dirt or debris from the damaged area with a commercial household cleaner and scrub brush. Use a wire brush to remove any loosened or damaged metal coating. Wipe down the area with a rag before continuing.
Measure the damaged area and add 4 inches to this number. Slip on a pair of work gloves and safety goggles before securing the galvanized steel sheet to a work bench with two C-clamps, one on each side.
Draw a template, according to the measurement taken earlier, with a permanent marker. Cut out the galvanized steel sheet with electric sheet metal shears. Work a piece of fine-grit sandpaper over the sharp edges of the newly-cut galvanized steel sheet.
Mask the area around the damaged section with double-sided butyl tape. Butyl tape provides a moisture barrier around the damaged area of the curved roof section.
Center the galvanized steel sheet over the damaged area so that it also covers the butyl tape. Attach the steel sheet to the roof with 2-inch metal screws and a drill equipped with a screwdriver bit. Space the screws at least 1 to 2 inches apart to create a tight seal.
Run a bead of silicone caulk around the sides of the patch to form a waterproof seal. Smooth down the caulk and work it into the gap between the metal roof and steel patch with your finger.