If your roof has a gentle slope and you are comfortable working on it, you can do the roof cleaning yourself, but keep the following in mind:
Team. You need a full body harness, a garden sprayer, a good size garden hose, and chemicals that are not toxic or corrosive; If the stains are severe, you will also need a special applicator and rinsing tools, but in that case, it is best to hire a professional service.
Do not use whitens. Many cleaning supply stores offer whitens as a special product for this cleaning, but it only removes surface stains without removing the underlying problem, and the stain will return in a few days.
Use sodium hydroxide products (bleach or caustic soda). Bleach works better than whitens and is less damaging to vegetation. But they are also corrosive and can cause burns, and their use requires that you put on all protective equipment.
Use the bleach and a brush to clean the stains. The bleach should work for a few minutes on each stain, and when all have been removed, rinse with a medium pressure jet. Brush if necessary to remove bleach residue.
Now it only remains to choose the day and time. Check the weather report and choose a cold or cloudy day but without rain.