Cupola

A cupola /ˈkjuːpələ/ is a small, most often dome-like, structure on top of a building. Often used to provide a lookout or to admit light and air, it usually crowns a larger roof or dome.
The word derives, via Italian, from the lower Latin cupula (classical Latin cupella from the Greek κύπελλον kupellon) "small cup" (Latin cupa) indicating a vault resembling an upside down cup.