Manual box window

I need a box window for house I'm designing. The auto Box window doesn't allow me to customize my windows.
So I built manual pop-out with floor height 24" above interior and placed a doorway from inside with casing removed to make clean opening.....worked fine but for the siding being removed from my main wall line below the two perpendicular box window walls....have had this challenge before. Where do I tell the program to keep the siding? I know I can alter my final elevations...but, at prelim stage sure is easier to plot a 3-d without changing it.

Not quite sure I understand compleatly, what is a manual pop out?, Here is a box window I built. It's just a room with another small room added for the window box. In this example I made the floor height 1000 mm. with a 1000 mm room height. I also reduced the thickness of the floor platform, to make it look less chunky, and to enable the windows to be set lower down. To open up the window box/room you could use a door, however I found it easier to work with a window, Muntins to zero, and casing suppressed.