How do I make walls go to the ceiling (see attached photos)

[Nate_M]

I'm drawing a plan for a second floor home office space that includes an elevator. The elevator is essentially a round tube with windows. I was able to closely recreate the look of the elevator by creating a round room with windows and a door. The problem I am having is that I cannot get the ceiling of this "elevator room" to go all the way up to the ceiling of the larger space it's located in. For some reason part of the wall goes to the ceiling, but other parts do not which leaves a weird gap around the top of the elevator. The entire space is a reverse gable, therefore it has a sloped roof/ceiling plane. I suspect this is part of what's causing my problem. Can anyone help me figure out how to get the elevator walls to extend all the way up to the sloped ceiling? I attached two photos to help illustrate my problem.

[DavidJPotter]

Draw the missing "attic wall" manually on the "attic" <A> level.

 

DJP