Hey there....if its any consolation, I have 13' ceilings in my main room. The dimensions of the room are approx. 25'w x 27'l x 13'h. I have had extremely great luck in this room. Its woody sounding and great for certain types of drums. Not All!
Any way, I would strongly advise a reflective floor with a treated ceiling. It's amazing how the drums open up when there's no rug (Garbage) or carpet under the kit!
I did the whole studio on my own after reading all the books like your doing. If money is not an object, then definately get the designer...a good one! If money is tight, I think doing it yourself can get some very good results. Other than a decent hump around 400 Hz in my room, I wouldn't change anything about it. Regards.
M