Desk Hutch for File Cubby Base Desk

Attach the top to the two outer sides and the center divider, using 2" screws, 3/4" pocket holes with 1-1/4" pocket hole screws, or 1-1/4" brad nails and glue — this joint gets reinforced by the back panel later, so any of these methods works. The open area's inside width is 27-1/2", not 21" — use the updated number.

Attach the shelving-area base and the open-area base (updated to 27-1/2" long) across the bottom. Nailing works, but pocket holes are worth using at the center for extra strength. No Kreg jig? Nail or screw in at an angle instead.

Add the shelving-area bottom shelf, then the three interior dividers — same fastener choice as the base supports.

Measure the assembled hutch's actual back opening, cut the backing material to fit, and attach it with 3/4" brad nails and glue.