You can create an opening in a ceiling using the Cut Opening tool. You create the opening by picking points to define its size and shape.
To cut an opening in a ceiling:
Select the ceiling 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 select the start point again.
Right-click and select Finish.