If it is heavy enough I would go to the trouble of removing it manually with perhaps the aid of plastic scrapers. Don't damage the roofing with pressure washing or a hose from the ground that would get up under the shingles.
One off I would from the top of the roof use a house wash that will gt rid of mold etc. I can't think of the name I want, right now.
You'll have to get rid of some of or all of the deep shade along with moisture is letting it grow.
I wouldn't want trees with the cabin in the fall line anyway but it does help keep things cool. So you might consider just some trimming or remvoal of clost trees.