Sand all edges of the wood to remove any splinters or rough spots.
Stand two 2-by-4-by-75-inch boards on the work surface horizontally, with the 2-inch side resting on the work surface. Place two 2-by-4-by-34-inch boards vertically at each end. Run a bead of wood glue along the ends of the 34-inch boards and sandwich them between the 75-inch boards to make a rectangle. Clamp the pieces together and drill pilot holes in the outer boards into the 34-inch boards every 3 inches. Attach the boards together with screws. Repeat two more times to make a total of three bed frames.
Place one 1-by-1-inch board on the bottom inside of each 75-inch side piece on the bed frames. Center the wood, leaving 1 inch on each end. Attach with wood screws every 3 inches. Repeat for each bed frame.
Place one 84-inch board flat on the work surface. Apply a bead of wood glue to one narrow outer edge of the board. Stand another 84-inch board on its narrow side and line up the two boards so the ends are even. Press the boards together and secure with clamps. Drill pilot holes every 3 inches along the edge where the two boards meet. Attach the boards with screws. Repeat three more times to make a total of four legs.
Place one bed frame, with the 1-by-1 board toward the bottom, on the floor in the room it will stay. Place one leg on each of the outside corners and hold in place with clamps. Drill two pilot holes 4 inches deep through each of the leg pieces into the frame pieces, for a total of four holes in each leg. Thread a carriage bolt through each of the holes and secure with a nut. Repeat for each leg piece.
Place one 1-by-2-by-34-inch cleat horizontally at each end of the frame. Place the cleat inside the frame so the wider edge of the cleats rests on the 1-by-1 boards. Screw these into place with wood screws. Space four more of these cleats, one about every 14 inches, along the 1-by-1-inch boards and secure with screws.
Measure from the top of the installed bed frame up 36 inches and make a mark on each leg. Have a helper hold the next bed frame so the bottom of the frame is at the 36-inch mark. Secure with clamps. Drill pilot holes for the carriage bolts the same as before and install the carriage bolts. Install the 1-by-2-inch cleats in the same fashion as for the bottom bunk.
Measure up from the top of the middle bunk 36 inches and make a mark on each leg. Lift the last bed frame in place so the bottom of the bed frame is at this mark. Secure the bed frame with clamps. Install the carriage bolts the same way as the other two and install the cleats along the 1-by-1 boards.
Measure 15 inches up from the bottom bunk. Make a mark on the legs at this measurement. Install a 2-by-6-by-34-inch board across the outside of the frame on the narrow end. Install between the legs with screws as a step to get to the middle bunk. Repeat between the middle and the top bunk as a step to get into the top bunk.
Sand, paint and stain as desired.