Lichen are not considered algae; they are a symbiosis of two or three different organisms and, if anything, would be more akin to a fungus since that is the main component of the lichen's "body." They do not feed on the material they are attached to, though, and merely use it as a surface to grab a hold of; the photosynthesis of the algae inside of them provides them with food. Lichen should not need removal (especially from tree trunks, and likely from roofs as well), but we specialize in home gardening and do not have training in materials care for roofing types. We would not expect lichen to damage a roof; if anything, its presence might help shield the roof a little from weathering. In either case, you may need to inquire with either an architect or the roof shingle manufacturer about the need to remove lichen and the best way to do so (if it differs from the instructions they already sent you). A diluted bleach treatment might damage the foliage of any foundation plants the solution drips onto below, but if diluted enough, it might not cause leaf dieback, and it would not be expected to kill anything unless a small annual was swamped in runoff. (Or, a dropcloth might be enough to block most of the runoff.)

Miri