Use Blue Coral Wash and wax with same amount of Clorox in a bucket and mix in some water. Apply with a bristle brush on broom handle. Wet first then wash front to back allowing mixture to stay on until all is done only rinsing if heat dries it before you are done. Blue Coral has 10% bees wax in it that preserves the roof by putting a coating on it as it builds every time you use it. It will clean evaporation pans in A/C units and preserve them too. It also works excellent on awnings and sides of RV. It's in Walmart in auto section about $3.95.