Put on boots with decent traction, as metal roofs are slippery. Don't work on the roof if it is wet. For extra precaution or if the barn has a steep slope, anchor yourself by tying one end of a rope around your waist and the other end to a tree or solid structure on the opposite side of the roof. Walk along the screw heads to enhance traction when walking on the roof. If the roof does not have sheathing, walk only along rafters.
Clean the seam areas using roof cleaner and a scrub brush. Remove any flaking coating or rust with a wire brush. Rinse with fresh water and treat any remaining rust with rust converter.
Paint any areas where coating had flaked away with roof primer and a paintbrush.
Remove screws along sheet metal and roof cap seams, using a drill with a socket bit. Apply consistent beads of metal roof sealant with a caulk gun under the laps. If the sheet metal is thin and flexible enough, you may be able to get the nose of the sealant tube under the laps without removing the screws. Replace the screws after applying the sealant. Allow the sealant to cure for eight to 12 hours.
Paint the seams with waterproof metal seam sealer. While the seam sealer is still wet, cover the seams with 4- to 6-inch strips of high-tensile-strength metal roof fabric. Paint a coat of seam sealer on top of the strips of fabric.
Inspect all other screws to locate loose screws. Tighten these screws and cover the screw heads with metal roof sealant. If a screw is stripped, replace it with a longer roofing screw.