Something that's pitched is slanted or sharply angled. The pitched roof on your cabin means that snow slides right off in the winter time.
You're almost always going to see the adjective pitched describing the angle of a roof. The sharply pitched roof on your grandparents' house might make the attic particularly charming, and the barely pitched roof of your garden shed could lead to a leaky situation in heavy rainstorms. Pitched comes from the sense of pitch that means "slope or inclination," but beyond that its origin is unknown.