Struggling with extended gable roof and ceilings

[David J. Potter]

To expand on what Jo Ann has said, you use the ceiling height setting to guide in your lower roof, in this case you use that setting to control the roof and then once you have your roof planes where you need them you turn off "Auto Build Roofs" and then change your ceiling settings to suit your finished model.
Some things (walls and settings) are temporarily set to get the roof result and when achieved you then leave roofs alone and finish your design.
You use the tools at hand to control and guide and then move on.

DJP