Edit Multipatch Face with Curves?

[GBacon]

I've created a multipatch for a large building and am trying to digitize and extrude a face on the top. I can create a cutout with a curve in it but cannot get the cutout (red below) to extrude as a whole; it grabs triangular slices and extrudes them rather than the whole shape, making my roof look like a TIN. Can this be done or do I have to create a second multipatch feature with a base at 325 feet (top of building) and merge it with the other feature?