Creating a Tray Ceiling using attic space

[PhilCrane]

Hi,

I have Home Designer Pro 2025 and am trying to create a room with a tray ceiling where the "tray" is actually part of the attic rather than the room. I've attached 2 drawings, the first is what I have created so far in Home Designer and the second is what I'm looking for. If I create a 10' high room I can then make soffits to get the shape I want but that leaves unwanted corners on the room (marked with x's on the first diagram. I want to remove these because the roof line I want cuts through the corner. The second diagram shows what I would like - the ceiling is 8' and the tray part takes up room in the attic and thus doesn't affect the roof line. Is this possible to create in Home Designer? It looks like it's possible in ChiefArchitect but that's way too expensive.

 

Looking at a post from a few years ago somewhere suggested creating a room within a room and setting the inner room at the required height but that still leaves square corners.

Thanks,

Phil