Draping surface or mesh on a revit model

Hi all,

So, I received a .dwg export from Revit. All elements on the same layer - shared cells, mesh for top of element, side of elements and bottom as well. I need only the top surface for the construction guys. Normally I would select one topmesh at a time and put it on a isolated layer, but it is very time demanding for bigger models.

So I got an idea to test if I could use some of the mesh tools to create a topsurface mesh more easily and smaller error risk...

I followed the steps: empty (3d seedfile) dgn, referenced in the .dwg, merge the needed elements in my file, dropped the shared cells (as the tools did not read it), now I tried 2 things:

1. Tool "Create drape mesh": almost did it, but I could only drape from z=0? and therefore I did a bottom drape, but I need a topmesh. Am I using the tool wrong?

2. Tool "Shrink wrap mesh": Did it quite good but wrapped it as promised - sides and bottoms included (please see picture below). Anyone knows if I can extract only the top from this wrapped mesh?

and several others...

Any experience on this or suggestions?

Thanks, Signe