Control Room Design Question

ok this has been making me ponder. when you use a ratio for building a control room. do you build it rectangular first(aside from the walls at 12 degrees), then add your false walls and ceilings and traps and what not. or do you design it so the ratios and construction are based upon the room AFTER false walls and ceilings are considered. in other words, if your room is 12 ft high, but when you add your false ceiling its only 8 ft high from floor to the false ceiling, thats ok right? the rest would still be based on 12 ft and not 8 ft?

generally speaking you can approximate the room raio with angled walls, or use a rectangular room and build it treatments. if you have a false ceiling overhead, typically you would use the real height of the room keeping in mind that the false ceiling will affect some frequencies depending on its construction.