Exactly What Determines Ceiling and Roof Height?

[rraisley]

Roofs continue to confuse me. I'm using Home Designer Architectural 2014. I'm presuming there is no way to change the "thickness" or actual material of roofs? They appear to be 2x6, without being able to be changed, is that right?

As to height, I know that I can select a Room, and from its properties determine the rough and finished ceiling height. I'm assuming that somehow that determines the height/location of the roof. But as each room could have a different ceiling height, or no ceiling, and that doesn't result in multiple roof heights. So what, exactly, determines the roof height (not pitch, the height at the walls of the house)?

Could ceilings even be several feet below the eves of a roof, like in a drop ceiling? If so, how is that accomplished? The difference between the rough and finished ceiling height is normally just drywall thickness, but would it be changed to 24" or something to do that?