Hi,
I think you can use this code (not tested):
BCOM.Fence fence = s_comApp.ActiveDesignFile.Fence;
BCOM.Element el = fence.CreateElement();
double area = el.AsShapeElement().Area();
The real code has to be a bit more complex, because CreateElement() doesn't always return shape element (see MicroStation VBA help for details). So I guess depending how the fence was created my code can throw an exception in some cases.
With regards,
Jan