Ceilings
In 2D plan views and 3D views ceilings are set as invisible by default, in order to be able to see into the rooms in the 3D views. If you therefore wish to see or edit ceilings, activate the ‘Visibilities’ dialog for the view and check the box for ceilings in the construction elements category.
More:
Automatic Ceilings
Deactivating Automatic Ceilings
Manual Ceilings
Properties of Ceilings