The coffered ceiling shape defines style. But the style of the end product also depends on materials and colors. White square waffle ceilings made with drywall project a minimal approach while stained wooden beams make the room more traditional..What matters when you’re laying out a coffered ceiling is the size of the finished beam, not the size of the crown molding. And you have to use the Outside Dimension of the full finished beamthe O.D.not the backing or substrate you might be installing first. I make my coffered ceilings using .