Working through the design for my first modern desert house with a flat roof. (See attached rendering, roof/ceiling plan, and roof detail.)

Definitely out of my comfort zone so any comments, advice or tips would be much appreciated. I want to take this to a structural engineer soon, but don’t want to be totally embarrassed. Not sure I understand joists and the structural implications totally.

– I’d like a relatively narrow profile flat roof – 11 7/8″ i-joists seem like they can span 23′. 

– I’m trying to achieve headers integral to the roof, so that the windows can go up to the ceiling by hanging i-joists to structural double rim headers. Joist extenders get the ceiling below the double top studs. 

Thanks guys!