Shed Dormer Help

[Seige]

I am working on recreating a shed dormer over a bedroom as pictured here.

But I cannot figure out how to properly draw it up. The closest I could do was lower the ceiling 30 inches, add it on in a 3rd floor, section off the dormer with invisible walls, and change the pitch over the window.

When I try to follow the directions for a manual shed dormer, the ceiling that I want to be sloped ends up flat instead.