I have also tried a sloped-ceiling octagon but I didn't like the outcome, so I haven't got any pictures to show.
Secondly, yes, this is the ground floor and above that there's another floor. This was never a problem since I always built the rough ceiling taller than the finished ceiling and the ceiling finish is quite thick, so that the finished floor is 2.7m
@ dshall: what is SOL? Am I the Sun? :-)