What are the causes of cracks on the outside of the roof of brick-concrete buildings?

First of all, you should be an architecture major, ask questions and get the answers you want.

My opinion is:

It depends on the actual situation.

The most likely situation I have ever seen is long and the length of the building is large. The roof temperature is high and the deformation is large, which causes inclined cracks on the outside of the roof at both ends of the building. Especially by the window.

This kind of crack is described in a book with common quality defects.