It isn't called anything. It is just called part of the nave.
Apse
VAULT
A pointy part of a church roof is called a steeple. Steeples are tall structures that rise above the roofline and often serve as a focal point for the building. They are commonly found on churches and other religious buildings.
church roof
Steeple
it is called a roof
The roof
Roof
It is what you called the planning for the roof.
A post that supports a roof is called a column.
The window in a ceiling or roof is called a Skylight.
The roof of a cave is referred to as the "ceiling" or "overhang".