you could do it in two steps -
- if you added the floor as a single plane, project the outline onto a plan and create the flat floor (so that revit is happy) you could then 2) modify the subelements of the floor to drop individual points on your floor down to the levels you have in rhino, like this : Modify Floor Subelements (SlabShapeEdit) in GHPython - #3 by eirannejad