Enclosed area on top of a building.
A penthouse can be an apartment on the roof or top floor of a building or a structure on the roof housing the top of an elevator shaft, air-conditioning equipment, or stairs leading to the roof. A penthouse is usually set back from the vertical face of a building, but as a real-estate term, penthouse may refer to any top floor, regardless of setbacks. Though the word now often suggests a luxurious apartment with a panoramic view, historically a penthouse was a lean-to, shed, or other small structure attached to a comparatively large building.