A sugestion for trimming your walls to multiple roofs:
Select wall and main roof, go to 3D window, perform trim (base).
Back in Plan, select wall and dormer roof, go to 3D window, perform trim (top).
Wall will now be trimmed to both roofs.
Alternatively, use SEO, you can select all roofs and dormer walls, assign targets, operators as necessary in 3D window, Subtract with Upwards / Downwards extrusion as applicable.
HTH