Sand four lengths of 2-by-10-inch lumber cut to 70 inches and three lengths of 1-inch-thick plywood cut to 30 inches by 90 inches for a queen-sized platform bed.
Varnish or paint the components of the bed before assembling them, and let them dry according to the recommended drying times on the paint or varnish label.
Position the four lengths of 2-by-10-inch lumber 26 inches apart, but parallel to each other. They should be resting on a 2-inch edge, with roughly 70 inches between the outer two planks.
Lay the plywood planks across the 2-by-10-inch planks with all their ends flush. The ends of the plywood should extend over the outer two 2-by-10-inch planks by 10 inches on each end.
Drive 2-inch wood screws through the top of the plywood platform into the 2-by-10-inch lumber underneath every 5 inches along the length of each 2-by-10-inch plank to secure the platform bed together. Place the queen mattress centered on the plywood platform to finish the bed.