Hi. I have a building that I import as a 3D-model (so it isn't generatred out of a footprint). The building gets higher as a stair. I assigned a rule to the building that makes an fence by extruding the top and then comp(f) the side. But this way it also creates a fence on the inner line (screenshot). How could i tell it only to extrude where the building stops to get higher so it would only have a fence where actually a terrace is?