Once you have created a deck, you can insert a custom opening in it of virtually any shape and size using the Cut Opening tool.
You create the opening by picking points to define its outline.
To insert an opening in a deck:
Select the deck by clicking on one of its edges.
Right-click and select Cut Opening, or select Edit > Modify Elements > Cut Opening.
Select a start point for the opening.
Continue selecting points to define the opening. As you select points, the opening is created. The last point picked is always connected back to the start point to form a closed shape, so you don’t have to pick the start point again.
When you have selected your final point, right-click and select Finish.