The cleanest look for a gable end with a closed eave is to angle the soffit therefore eliminating the need to resolve the eave at the gable end.
Frame gable roof soffit.
The other end will be closest to you.
Ridge work out how wide you want the barge soffit boards.
This is how i did my pole barn workshop and at the end of the video i also show.
Before you nail it slide it a tiny bit out from the back of the f channel approximately 1 16 inch.
This configuration gives the look of an open eave but it has the same benefits ease of maintenance and energy performance as a closed eave.
This is a very small amount but it will keep your soffit from bending later.
New roof system will need to be able to accommodate weight of snow drifting against existing wall or sliding off from roof depending upon whether reverse gable will be added to endwall or sidewall.
With enclosed overhangs soffit will attach to this solid blocking.
Here s how to frame a boxed soffit on the eave and gable end of a building.
Set out the wall plates to whatever centers you need for your gable roof 400 450 600 or 900 governed by the weight of roof covering ie tiles and cut fix the joists so they are parallel to each other and flush with the back edge of the wall plates.