To create a hole in the floor of a room, you have to insert an object (Create Object) with the dimensions of the hole that you want to create, assign it a height of 1", and give it an elevation of -1" to place it in the floor. Next, click on the border of your newly created object in the Layout window and activate the Hide option from the Property Grid.
You may need to refresh the scene in the Virtual Navigation window. Use the Update View button in the Navigation tab of the Ribbon:
Here is an example of the result:
You can follow the same process to create a hole in the ceiling but in this case, the elevation of the object should be equal to the height of the room.
This article is valid for the 2017 version and later.