Hey Karl...
(I think we met at the 8.0 demo in cda....at least I remember someone in Sandpoint)
The Revit tool is like the mesh tool you show, but when I mean by slab, when you specify a bottom elevation, the whole bottom is at that point....
Now, I remember somewhere/somehow with Mesh, I could bring the bottom of the mesh up....
Such is this, I have a mesh that has an elevation from 971' to 972', I dont want a thickness down to 0'. I thought in 7 you would do -100' or something like that....but I cannot get it to work in 8.1....