Here's what I use:
https://www.amazon.com/dp/B001FCB0ZG..._t1_B000BRJURG
Get a quart spray bottle and a stiff brush (not a soft wash brush). Wet down the roof and spray a 4x4' section with the cleaner. Scrub with the brush, wait a few minutes, then scrub again and rinse off. The roof cleans up to look almost new. A few stubborn mildew spots or stains may remain.
I clean ours about twice a year. I don't use a roof treatment afterwards. As long as the roof is kept reasonably clean and has no tears, it will outlast the rest of the 5er. Washing every six months means you can inspect it, reseal where needed, and catch any issues before they become a problem.
Dave
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Dave, Barb, and Paisley the Wonder Wiemeraner
Was - 2015 3160RL Legacy Edition & 2014 F350 6.7l PSD SRW Platinum
Now - SOB