Forgive me if everyone else already knows this (I can be slow sometimes).

If you use the construction line from the shapes toolbar you can automatically find edges of walls. eg, if you have a cavity wall say brick/cavity/insulation/block, when putting in a construction line it automatically snaps to the edge of each component (or you can use dynamic input to offset from an edge). This allows you to then trim to an edge rather that to the base line of the wall.

This works on curved walls as well as straight.

Also its quite nice that the construction line automatically gets put on a layer that doesn't plot.