the outside face of your window should be placed on the level zero plane and that the Wallhole slab should be flush with that plane.
Create a wallhole slab in the same shape as the window. Create a typical slab, put it at zero. Select the slab, go to Tags and Categories tab in the dialogue box. Under "ID" type "wallhole". I made mine .25 " thick, or maybe even 0 thickness. Make sure all components are stacked at zero level otherwise the window will be far away from the actual hole in the wall in the plan and other views.
Mine worked fine after I had a little help from GS support. The help menu is missing the wallhole slab step.