At this time you can not combine layouts. However, you can create wall groups for multiple layouts and then insert them into the same layout.
To create a wall group select the Tools icon from the vertical toolbar.
Select the Create Global Wall Group option.
The software will then prompt you to Select the walls from your layout that you would like to save.
After the walls are selected click Enter.
Give your selected wall group a Model Name, Option Name and Description.
Click Save and you will then be prompted to save the wall group.WGD file to your computer/server.
After the file is saved you can now use the Insert Global Wall Group icon to add wall groups to any of your layouts.