The best way will probably be to use a Solid Element Operation with the wall as your target and a roof (at the slope and position you want) as the operator.
Then "Subtract with downwards extrusion".
You can hide the roof in a layer that can be turned off.
Don't delete it as the SEO is a live operation so delete the roof and the trim is deleted as well.
On the plus side you can move and adjust your roof to adjust the trim.
Barry.
One of the forum moderators.
Versions 6.5 to 27
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