When painting corrugated metal roofing, there are important steps to follow. The first step is to clean the roof thoroughly. You can use a pressure washer to do this. Then use a wire brush to remove remaining rust. Next wash the entire roof with a bleach solution, rinse, and allow the roof to dry completely. Then apply a quality primer and allow it to dry before moving on. Once the primer is dry you can apply the paint. Let the paint dry completely between coats, and apply at least two coats. Do not paint if rain or low temperatures are expected, as that may cause the paint not to dry properly.