Various plans on the Internet offer material lists and instructions for making cupolas, which are roof structures, usually designed as squared domes, that can be used to decorate a roof or--in the case of older home construction--serve as a roof ventilation opening for the house. Most plans feature decorative cupolas, but a functional cupola can be added by opening the roof.
The cupola consists of a few basic parts: the saddle, the vent housing and the roof. The saddle is the lowest part of the cupola that sits directly atop the roof. It is crucial to build a solid saddle, because this part of the cupola bears most of the structure's weight. The saddle is usually constructed by measuring the pitch of the roof and then assembling the walls of the saddle based on that measurement. The saddle is installed as a single piece. Above the saddle is the vent housing, a large frame built with downward-facing vents installed on each side. Sills bracket the vent housing above and below, and it is recommended to bevel the edges of the lower sill to prevent damage from water build-up.
Finally, the roof is built and then installed. The roof is arguably the most decorative part of the cupola. There are a variety of styles that the roof and cupola can take on, depending on the architecture of the house.