If the roof is a single arch, Solid Element operations will trim it as you like.
As for this being an unfortunate work-around, it will have to do until Archicad has a read-everyones-mind-for-all-possible-ways-to-make-a-thing tool.
If the roof is a curved arch, a simple curved wall extrusion with the complex profile gives you the solution without trimming.
To have the SEO elements disappear and a proper plan symbol created, convert the elements into an object and hide the layers for the trimmed roof and the SEO element. [for future element updating]
As for finding my relevant posts for the complex profile, try searching the combination of "complex profile" and "Dwight"
Most useful among the returns are:
complex arch dome segments
another one
and yet another
Dwight Atkinson