Use the Ceiling tool to create a ceiling in a reflected ceiling plan view.
Open a ceiling plan view.
Click Architecture tabBuild panel (Ceiling).
In the Type Selector, select a ceiling type.
Place a ceiling using one of the following methods:
Use walls as ceiling boundaries
By default, the Automatic Ceiling tool is active. When you click inside walls that form a closed loop, the tool places a ceiling within those boundaries. It ignores room separator lines.