When building a shaped control room, ratios that apply to rectangular rooms don't necessarily apply anymore - depending on the kind of shape. For cockpit / non-environmental / FTB rooms, they don't matter much at all anymore. Of course, your room still needs to have proper dimensions, but for other concerns than purely modal behaviour.
If you decide to build such a room, don't forget to leave a lot of space for the treatment on/of side walls and ceiling and think about the fact that LF surfacic behaviours is amplified in shaped rooms. Beware of treatment near and behind your backwall diffusors. You have to manage the LF energy that will go through them and avoid having re-emission and resonances there (which happens everytime and has to be adressed!).
Also it gets real complicated to calculate pressure points in shaped rooms, but take the time to do it right and pay close attention to all that during build.
But IMVHO, unless you know exactly what you're doing, I wouldn't put my fingers into room shaping - leave this to a designer, as it's so very easy to miss it.
Keep us posted!