Is it possible to create a room with a ceiling that follows the pitch of the roof?

A ceiling that follows the underside of the roof is sometimes referred to as a cathedral ceiling, and can be created by disabling the flat ceiling setting within a room specification dialog.
the plan in which you would like to create a cathedral ceiling.
tool, click inside of a room you want to have a cathedral ceiling, and select the Open Object
edit button.
In Home Designer 2024 and newer versions, flat ceilings can also be removed by selecting a room and clicking on the Turn Off Ceiling edit tool.
