Make plans to build a bunk bed using an online template or a blueprint from a how-to book or magazine. For a custom bunk bed, design an original plan using graph paper, assigning each square a particular measurement, such as 1/2-foot per square.
One plan for an easy-to-assemble wooden bunk bed starts with two 41.5-inch and two 78-inch 2-by-6 boards that create a rectangular mattress frame. Use 3-inch deck screws to secure the pieces together. Repeat this step to create the second mattress frame. Take four 38.5-inch 2-by-4 boards and secure them with deck screws and finishing nails into the bottom of the first mattress frame as support joists with an equal distance between each board. Repeat on the second mattress frame.
Take four 68-inch 2-by-4 boards and secure them with finishing nails to the mattress frames at 1 foot high and 4 feet high or at a height that suits whoever uses the bed. Drill carriage bolts with washers on each side of the wood into the corner rail connections of each mattress frame. Make guard rails using 41.5 and 78-inch 2-by-4 boards. Secure these on the top bunk at the corners with deck screws.
Use two 38.25-by-74.75-inch pieces of 3/4-inch plywood as mattress decks and secure them to the support joists. The frame is complete and only needs mattresses and a ladder for the top bunk.