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.
From the DomuS3D 2019 version, this procedure has been temporarily changed. When you want to create a hole in the floor or ceiling, you must reverse the normals of the drilling object. Open the virtual navigation and select the object, the right-click and select the command Flip Normals. Next, click on the border of your newly created object in the Layout window and activate the Hide option from the Property Grid.
This article is valid for the 2017 version and later.