Set up a sturdy ladder so that you can safely reach the roof. Be sure that both legs of the ladder are firmly planted on level ground.
Use the wide push broom to scrub off all heavy dirt, moss or algae accumulations on the roof's surface.
Pour a 50/50 mixture of warm tap water and bleach into the garden sprayer and secure the cover. Be sure to wear work gloves to prevent bleach from coming into contact with your skin.
Prime the garden sprayer by using the pump on the top of the cover. Be sure to follow the manufacturer's instructions when operating the sprayer.
Apply the bleach solution directly onto the roof, using the spray attachment on the garden sprayer. Be sure to wear eye protection to guard your eyes, should the solution blow into your face.
Rinse the bleach solution from the roof with a steady stream of water from the garden hose after the solution has worked on the stains for 15 minutes. Allow the roof to dry completely before continuing, to avoid working on the slippery wet surface.
Attend to tough remaining stains by re-applying the bleach solution, waiting 15 minutes, scrubbing the stain with the push broom, and rinsing away the debris.