Board and Batten Bunk System — Top Bunk

Build the two panels — plywood/MDF/particle board with the 2x2 top and 1x6 bottom trim. Drill the pocket holes you'll need for attaching the legs in the next step now, while the panels are still easy to work.

Attach the legs to the panels with pocket holes set for 3/4" stock and glue, using 1-1/4" pocket screws. Also attach to the header — a pocket-hole set for 1-1/2" stock with 2-1/2" screws is stronger there, though a 2" nail works if your panel pocket hole is at the top.

Drill the side-rail pocket holes set for 3/4" stock and attach the 1x6 rails to the leg assemblies. Important: if an adult or a large child/teen will use the top bunk, use bed-rail brackets here instead of pocket holes — the extra load warrants the stronger connection.

The guardrail is optional but strongly advised on a top bunk. Drill one pocket hole on the inside of each rail and one on the top of each end, plus two on the ends of the bottom boards, and build the guardrails. Attach them directly to the side rail with bolts, nuts, and washers — not screws — placing the bolts symmetrically. A guardrail is the one part that must never work loose, which is why it's bolted.

Attach the 2x2 cleats to the inside of the side rails, then either lay a bunkie board across them or add 1x3 slats spaced to your mattress recommendations. Screw the slats down with 1-1/4" screws and NO glue, so they stay removable for cleaning and mattress changes.

For the decorative board-and-batten look, add the 1x2 headboard battens across the panels with glue and 1-1/4" finish nails, evenly spaced. Fill holes, sand, and finish or paint.