In typical situations, windows are set in from exterior wall corners to allow room for structural framing as well as for the casing, or trim molding. Occasionally, though, windows are placed all the way in the corner.
To move a window into an exterior corner
If you have not created the windows, select Build> Window> Window from the menu, then click once on one side of the corner where you want to create a corner window unit.
Make any needed changes to the window using either the edit handles or the settings in the Window Specification dialog.
When the window is edited as needed, click on it to select it, click the Copy/Paste edit button, then click on the other wall forming the corner to place an exact copy at that location.
Select Edit> Default Settings from the menu and in the Default Settings dialog, select Plan from the list and click the Edit button.
In the Plan Defaults dialog, check the box beside Ignore Casing for Opening Resize and click OK. In the Default Settings dialog, click Done to close the dialog.
In either floor plan or a 3D view, click on one of the windows to select it.
Click and drag the window all the way into the corner.
Repeat this process with the other window to create a symmetrical, mulled corner window unit.
Select 3D> Create Perspective View> Full Camera from the menu, then click and drag a camera arrow towards the corner windows to see the results.
Placing windows in a corner overrides the placement of wall studs that may be structurally important to the final design. For actual construction, special engineering may be necessary.