Picture of corner trim as installed.
Gable end siding shiplap.
A three person team two installers working from staging who feed measurements to another worker at a cut station on the ground can side a large gable end in an hour or two.
The peak is the tricky part multiply half of the overall wall length 12 by the vertical distance from the wall height to the peak 8 to get the gable end s square footage 12 x 8 96 sq.
The corner trim gives a solid edge to fix the siding up to and it also gives some end protection to the end grain.
Instead of simply running the siding material all the way up we often use shiplap boards to set off the gables.
Then add 20 on the gable to cover the waste of all those angle cuts 96 x 20 115 sq.
The inside covering of the gable end walls will eventually either be drywall or wood shiplap boards.