If you are in virtual navigation and can no longer see the ceiling, it is probably due to the walls of the room having different heights.
Right click on any wall and select Height. Type the desired value and select "Apply to all walls of the room".
If you are drawing the floorplan for an entire apartment and would like to design balconies or outdoor spaces with half-height walls instead of railings, it is recommended that you do this by constructing a wall object, so as to not cause the ceiling to disappear.
If you deliberately changed the height of one or more walls to create a specific design, such as a drop ceiling or a sloping roof, follow the directions found here.
This article is valid for the 2017 version and later.