gambel roof with no wall height - similar to 'A' frame

[Katalyst777]

Combining the instructions in both articles Lamina provided should work for you, based on your description.

Just set up your walls correctly to build a Gambrel roof, and temporarily set the Finished Ceiling Height in the room to be lower until after the roof is generated correctly.

Then you can uncheck Auto Rebuild Roofs and set the Finished Ceiling Height back to the default.