Switch to the "RCP" view (means Reflected Ceiling Plan; shortcut key:2) in the bottom left corner to enter the top view. Select the top surface and click "Customize Ceiling" to enter the ceiling interface. (or you can also click "Customize-Customize Ceiling" from the left catalog and select the top surface to enter the ceiling interface). Select gable roof or pitched roof from "Ceiling-Parametric Ceiling-Other" on the left and drag it into the room. The ceiling will be automatically applied to the room, and you can adjust the parameter of rotation angle, slope, the size of the ceiling from the right property panel.
