Depends upon what type roof material you have, and how dirty it is. Ours is TPO, and I just use Palmolive liquid dish soap with a scrub brush once a year. We store it inside from December 1st to end of March in a temperature controlled warehouse, so it doesn't get that dirty. However, this year, because of the extremely wet summer, had aphids drop their stuff on it which is very sticky and I guess sweet, because the yellow jackets and flys swarmed all over it. Really got dirty. I only used the Palmolive to clean it, did an okay job, would like to see it whiter. Maybe someone with more experience can offer a better cleaning material. I was thinking about a product like Clorox bathroom cleaning fluid, but gun-shy about using bleach on TPO.