I'm having trouble creating a form as a mass. Initially, I created it in Rhino and imported it into an In-Place mass as an SAT. First attempt was a fail because Revit couldn't do Wall-by-Face on the end parts. So I tried a few other ways of creating the geometry in Rhino. Revit either couldn't create the Wall-by-Face or couldn't even create the geometry.
So I decided to create the mass as a Revit Conceptual Mass. There I'm having trouble even creating the mass from scratch!
I've been using splines, but I'd be happy to approximate the edge curves as tangent arcs. Anything that works at this point. As you can see it is essentially a flattened half-cylinder with squished quarter spheres.