Extracting 2d silhouettes from urban model

I have this urban model with mesh buildings. I need to simplify them to a silhouette with courtyards. I extracted the outer shape (ConvexHull), but can´t do the courtyards (tried intersecting the original building (converted to surface) with the footprint silhouette as a surface). Any idea?

I attach the gh file with the internalized geometry.

Buildings_Redrawing.gh (237.2 KB)