You can also try the following python script - it has the command-line option to either have the buildings stop at the first point they touch the surface, or be just embedded into the surface. It works with either mesh or surface volumes and can project onto either surfaces or meshes. There is currently a limitation with volumes that cross the outer edge, so the surface to project to should be larger than the volumes projecting onto it.
ProjectVolumesToSrfs.py (5.2 KB)
–Mitch