Algae - the dark streaks
The most common by far. Airborne, lands everywhere, takes hold where there is moisture and shade, and spreads downhill with the water as dark streaks. On concrete tile it is cosmetic in any reasonable timeframe. On shingle it arguably holds a little moisture against the granules, but the sun is doing far more damage to the shingle than the algae is. Low-pressure cleaning removes it; it comes back over years.
Lichen - the crust
Grey-green, raised, crusty patches that grip the surface hard. Lichen is a partnership between an algae and a fungus, and it anchors itself into the surface it grows on. On shingle, that means it is holding granules, and stripping it aggressively takes the granules with it. On tile it is mostly cosmetic but stubborn. Lichen is the one that justifies careful chemistry rather than force.
Moss - the cushion
The soft green pad that appears in permanently damp, shaded spots - the north side under a tree, the bottom of a valley. Moss holds real water, like a sponge, against whatever it is sitting on. It is the least common of the three in Palm Beach County and the most worth removing when it appears, because a wet sponge on a roof is a wet sponge on a roof.
The thing that matters more than any of them
Debris. Leaves and organic material sitting in valleys, crickets and behind chimneys. It holds water against the membrane and blocks drainage, and it does more harm than all three organisms combined. It is also the easiest to deal with: it gets cleared, by hand, on a maintenance visit.
A word on the word
You will hear all of this called "mould". We describe what is on your roof as algae, lichen or moss, because that is what it is, and roof growth is a roofing matter that we handle under our contracting licence. If something inside the house needs a different specialist, we will say so.
Accessible valley and cricket debris clearing is included in both plans. Cleaning of surface growth, if you want it, is arranged through a vetted low-pressure cleaner.
Compare the plans