can i use this on my garare roof. Am surrounded by neighbors trees. they will not trim them , I have asked and its useless

Try "Wet and Forget" sold at Lowes. It is a blue liquid that you add to a pump sprayer 5 parts water, 1 part w-n-f. The only prep is the surface must be dry. This product is safe on most surfaces I apply every 6 mos and it takes care of the moss, algae, mildew and mold. Wind and rain are what activate the product.