Connect the pressure washer to a water hose. Turn on the water hydrant. Plug in the pressure washer.
Clean the metal building with back and forth passes of the pressure washer water stream. Work your way from the top down. Let the building dry.
Paint a thin coat of oil-based primer over the entire metal building surface.
Clean the paint brush with paint thinner. Oil-based primer and paint can be cleaned only with gas or paint thinner.
Allow the primer to dry for 24 hours. Paint the entire metal building with a thin coat of oil-based paint in the color you choose. Allow the paint to dry for 24 hours.
Paint the entire metal building with another thin coat of the oil-based paint.