I've been building coffered ceilings for about 15 years; they're great for transforming rooms into special places. My typical approach is to use built-up beams trimmed with crown molding to divide a room's ceiling into a grid with nine paneled sections.
Over the years, I've tried a lot of different beam designs and panel details; sometimes I design the center section so that it's larger than the others. But in general, the nine ceiling sections are of roughly equal size. In my experience, that means the room's overall length and width have to be within about 5 feet of each other.
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