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How to build a tray ceiling
Attach drywall to the entire ceiling.
Cut drywall to size with a sharp utility knife and a straightedge. Smoothen the edges of the drywall with coarse sandpaper and a sanding block.
Utilize homemade 2-by-4 t-braces to assist yourself and a partner when installing the drywall. Rent a cradle lift for assistance if you are installing the drywall panels yourself.