Hi Kayaker,
in 1-2-5 roof calculation use function 3-04 Priority of intersection to define different intersection priorities for each building outline. The higher the number, the lower the priority of a building outline. In this case, use priority 2 for the dormer, and priority 1 for the main roof.
If the dormer currently does not have its own building outline, you can use the function 2-07-3 Explode to extract a building outline from the dormer.
Best regards,
Jens Krause
Dietrich's Support