When the fascia on a gable end of a roof does not wrap the corner, the end is mitered. You can specify the mitering option: vertical, horizontal, or perpendicular.
The mitering options of a fascia can not be changed if the fascia either wraps a corner, or is not on a gable end.
 Roof Fascia panel
Roof Fascia panel
 (Modify Mitering).
 (Modify Mitering). 

Vertical miter

Horizontal miter

Perpendicular miter
Gable end fascias are mitered to match the rafter cut of the roof.
