Coffered ceilings are a great idea. This was a house in Hayward. To begin, we sanded 3/4″ plywood ripped on a table saw cut costs significantly over solid boards (1″ x 6″). These channels were assembled in the room, puttied and caulked, and anchored across the floor beams with mounts inside the channels. The perpendicular channels were then mounted to the anchored channels. They were painted and primed before installation, and caulked and touched-up once installed.