Yes, you can place a geometric shapes under your construction. Adjust the level elevations if need be. If your 0 level is below terrain, you may need to place the shapes around your construction (see SF 3D models 299 for a couple of examples). If not, the shapes will fill the basement too.

In the latest version of SH3D (5.0) you can also do more with levels (same elevation, show hide), which (in addition to grouping the geometric elements) can be useful when working with terrain.

ok