When you have a small room with a low ceiling height within a larger room with a higher ceiling height you can create a ceiling shelf above the smaller room.
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Ceilings
10294 - Saguaro Tray Ceiling
69 - Ceiling Basics
35 - Interior Soffits
5521 - Sloped Soffits & Coffered Ceiling Soffits
309 - Drawing Vaulted and Curved Ceilings
99 - Automatic Trey Ceilings
300 - Creating a Coffered Ceiling
64 - Using the Shelf Ceiling Room Structure setting
311 - Creating a Suspended or Dropped Ceiling
10203 - Ceilings: Vaults, Barrels, & Treys