Mass model loft

[Anonymous]

I have a problem with mass model, I think I can best describe it with the attached picture - when I make a loft between two splines on different levels (pink and blue), a straight edge (green) is created between their ends. I dont want it to be a straight line but another spline - red. I know thats how loft works, in AutoCAD I would probably just draw four splines and use EDGESURF command instead, but in Revit I cant seem to be able to make a surface out of a closed shape, because that requires me to place two points in the same place and that results in an error. 

[Anonymous]

I cant edit the post now, but I found another problem - I can't form a roof out of the mass model. I had to split the mass in two parts (when I select all splines it gives an error) and roof only works on one of them. I can use mass to wall, but I wont be able to trim walls beneath it this way.. 

[Sahay_R]

Try this -

create your model in Autocad,

import it into a Revit Mass family,

place it into a Project,

then create Roof>>By Face.