The way CD3's FloorplanCreator creates walls for the maps it produces is a bit odd; it draws a 1 foot outside wall directly on the roof profile. This not only puts half the wall outside the roof profile but most real world roofs I've seen have an overhang of at least 1 foot so rain doesn't run down the outside wall. In the next edition of City Designer the Floorplan Creator should have two additional fields ("Wall Thickness" and "Wall Offset") with the wall being drawn offset from the building footprint by half the thickness + the offset.