Connecting a flat ceiling to a vaulted ceiling

[MKredesign]

I am working in a floor plan where a flat ceiling changes to a vaulted ceiling. I have both ceilings built but I can't figure out how to close off the area where the two ceilings meet. Is there a tool I can use to close/finish off that gap so you don't see the roof above the flat ceiling?

[DBCooper]

Normally, Chief will automatically fill that space with a wall for you.  The easiest way to do this is to use a room divider and then just mark one room as not having a flat ceiling.  Since it looks like you want to show a partial wall you could use a half-wall instead.  In the picture below, I used a combination of a half-wall and a room divider. 

 

If you need more help, you might want to post you plan.