Thanks for your reply! Maybe I wasn’t clear enough with my original post, but I am not sure that is what I am needing done sorry. I have attached another snip of my example, with a bit more of an explanation of what I am after. Essentially I want that squared section to not be in line with the fascia on the gable end, and rather the gable wall. Following your steps, all that raising the fascia seems to do is raise or lower my entire roof.
Ive also attached (a very small, sorry) example of what I am trying to achieve. Doing a Google search, I couldn’t find many examples of what I am trying to do, however it is a very common method of construction in Australia.