Some signs that your roof needs cleaning are:
Dirty, stained, or discolored roof
Black streaks, green patches, or white spots on the roof
Loose or missing granules on shingles
Cracks, curls, or buckles on shingles
Leaks, mold, or mildew on the roof
If you notice any of these signs it may be time to meet with a professional to restore your roof's safety and appearance.