Expanding existing roof surfaces

The shortcut menu of a roof surface contains the Reshape Surface Element, Architectural Area tool. You can use this tool to change the outline of an existing roof surface by adding a new outline. In doing so, you can use the Properties palette to change the parameters taken from the existing roof surface, such as the height. This works like creating a new roof surface. After you have defined the polyline, you can adjust the edges. The new outline is part of the modified roof surface.

You can find the Reshape Surface Element, Architectural Area tool in the Change task area, too.