Busy hands are happy hands. ;)
I too had trouble getting my head around all of the compound angles present in the window structure(s).
Get one angle right and the rest look wrong. Change that one, and then parts don't quite fit anymore. Re-cut, and then test fit again. And again, and sometimes yet again. Getting these angles to approximately correct was harder than building my throttle.
The mitre box and the adjustable jig saw had quite a workout with this area of the build.