Queen-size platform bed sized for a standard 1525×2030mm mattress with 5mm of breathing room. The frame is plywood box construction with a center support beam and 12 slats spanning the width — more than enough to handle a heavy queen mattress and two adults without sagging. Total height to mattress top is around 350mm, leaving useful under-bed clearance for storage tubs.
This eats two and a half sheets of plywood. Cut the side rails first as they're the longest pieces and benefit from a track saw or a long fence. Glue and screw everything — nothing about a bed should be relying on screws alone five years from now. The headboard isn't included here; design that separately and bolt it to the bed frame after assembly.