Still using Chief 10, but here is what I do.
First, build the main roof.
Next, draw two temporary walls where you want the new roof planes to start. ( Earlier in my life, I drew the temporary walls about 12" long. Now, with I make them about three feet long so I can see them. Remember the Chief Viewing Caveat: Monitor Size =10x eyeglass prescription) These walls are perpendicular to the main roof, so the resulting roof will be a reverse gable.
Draw the reverse gable roof from those two temporary walls. Check that the top of fascia, etc. for the new reverse gable is the same as for the main roof.
Erase the temporary walls. Now the reverse gable is just sitting there pretty much not attached to anything..
Click somewhere on the main roof then the ridge of the reverse gable roof to show where the ridge of the reverse gable will intersect. An "X" will appear like magic on the main roof, and this will be where the Reverse Gable roof meets the Main Roof.
Extend the Ridge of the Reverse Gable to the intersection point.
Pull back the edge of the roof at the bottom so it sits on the exterior wall.
Adjust the overhang so it aligns with the main roof overhang.
Put a hole in the roof where you want the reverse gable wall to extend up to the reverse gable.
You will have to play with the roof hole (use separate window to see both 3D and 2D simultaneously) to allow the wall to penetrate but not extend beyond the roof lines.
Having said that, I can't wait until later today when I am ordering X9 and it comes with the "Put a reverse gable here, with cupola, shake siding, metal roofing, different roof pitches, two skylights "Trump Is My President" banner and built in telescope (for star gazing) " button. I sure hope the dialog box pops up with the option for telescope focal length.
As a great Philosopher once said "A plan design should exceed a CAD program's ability, or what's frustration for?".