"designed to be seen from below like the cupolas of Chambord"

The royal Château de Chambord is one of the largest and best known of the numerous châteaux situated in the Loire Valley in France.

It was built as a hunting lodge for François I who wished its roof structure to imitate the skyline of Constantinople.

A cupola is a dome-shaped structure built on top of a roof or larger dome in order  to let in light or air, or to act as a lookout point.

 

Château de Chambord and its numerous cupolas
Creative Commons AttributionChâteau de Chambord and its numerous cupolas - Credit: oletourn, Flickr

As previously noted, Brideshead Castle is partially modelled on Castle Howard in Yorkshire, which is a domed building.

 

Castle Howard's dome and cupola
Creative Commons AttributionCastle Howard's dome and cupola - Credit: Jordanhill School D &T Dept., Flickr