But I think it could be embellished a bit. In my opinion, cupolas are ornamental structures placed in a prominent position, usually at the top of a larger roof or dome. They often appear as small buildings in their own right, like diminutive temples perched on top of a building. They can be the small dome that crowns the top of an outdoor garden pavilion, folly, or gazebo. Sometimes the pavilion itself is called a cupola, especially when it takes on the form of a small, round Roman temple with a dome.
Cupolas occasionally act as the main roof of a tower, spire, or turret.
When they do, they usually provide a considerably more elaborate enclosure than the average roof. Cupolas on roofs may be accessible from the inside, commanding a high vantage point from which to look out over the world. When they are perforated with windows for illuminating the spaces below, they are also known as lanterns. This type may or may not be accessible from the inside. The Cupola Picture section of this website has many examples of buildings with cupolas, domes, lanterns, belvederes, gazebos, and belfries.