You had the same condition as I where the rake/gable steps back. I couldn't figure out a proper detail either so I ended up eliminating the step by extending to a single rake/gable which was probably better in my case. Maybe you silicone the heck out of that, then cover it with a little extra metal set in silicone to prevent the uv from ruining the exposed silicone joint.
There’s a gentleman in our town that builds them from scratch. They are called steel pole barn trusses, I believe they are made all over the country too.
