Intersecting full roof gables, need different pitch

[CDS]

Create a second floor.
Make the ceiling height 0"
Offset the 2nd floor gable walls slightly.

Not quite what you want but close.
Maybe further playing with pitches and/or ceiling heights?

The important thing is to keep that slight offset. That's
all the program needs to get that second pitch information
from you.

Maybe someone else (David?) can refine this or come up with
a more elegant solution...