To create a Site Model you require 3D data for the spot levels of the…
Vectorworks Tip 424 – Where To Put Site Modifiers
Many uses believe that the only place that you should store site modifiers is on the same layer as the site model. While this works very well, it is not the only place that you can locate your site modifiers. The site model settings dialog box allows you to choose where site modifiers can be located. They can be on the same layer as the site model, on any layer, on visible layers, or you can select which layers you want to put your site modifiers on.