Topo in Revit has several issues that make it difficult to manage. One of these issues becomes quite obvious if you ever try to model Topography on the top of a building or any other structure. It can be done, but the result is that the structure is full of Topo…
Essentially, there is no way to define the bottom extents of Topo. So while Pads can be used to push Topo down, there is nothing that will push it up or create a void in the middle of it. And since Topo defies all the rules of typical Revit geometry, this also cannot be done with in-place Voids.
So how do you model the “Topo” on top of the structure? One of the most commonly used workarounds is using Floors or Roofs. They work quite well if you have a consistent thickness, but you can also Shape Edit them via Modify Sub-Elements to create a more topo-like surface.
This Floor has a thickness of 10 feet, which when combined with an In-Place Void, allows the Floor to have a varying thickness. For some reason, once the Void cuts the Floor, its hatch pattern disappears in section (to turn it back on, I had to override by Element).
The worst part of this workflow, is managing the seam between the Floor and the Topo. Ideally, you would want to eliminate the seam or at least make it as small as possible. You also do not get contour lines from Floors, so if you wanted them they would have to be drawn in manually.
With some overrides (in Section) and edges turned off (in Realistic Mode), the final result isn’t half bad, though the Floor is not quite as smooth as the Topo around the edges.