I'm trying to see what people do for inside doors for the center of the bus. I'm not doing a roof raise so I wanted to see how the top of the door fits so there is no gap if you can but also were you won't have to duck for any frame. I have never built door frames so I don't know if what I'm asking is possible or not.
Why is it necessary to go all the way to the top, or bottom for that matter? Are you trying to seal a room off for some reason? Interior doors don't really need to do anything but block view, or rarely lock to keep someone out.