[header] How to build a tray ceiling [title] Attach drywall to the entire ceiling. [substeps] 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.