Connect the 2-by-6-inch boards at the corners, overlapping the shorter pieces with the longer pieces, using 3-inch drywall screws. The total length of this bed frame should be 78 inches, with a width of 40 inches.
Cut the 4-by-4-inch lumber into four pieces that measure the desired height of the bed. For a couch or shelving, this might be shorter, whereas a loft intended to house a full desk or other equipment below might be taller.
Place the 4-by-4-inch boards into the corners of the bed frame and bolt them into position using 4-inch lag bolts from the ends of the bed.
Cut the 1-by-3 1/2-inch boards into two pieces that measure the height of the bed when placed at a 60-degree angle. Cut the bottoms of the boards to this angle so that they lie flat against the floor, and cut the back of the boards where they will meet the bed at a 90-degree angle so that they lie flat against the bed frame. Using 2-inch screws placed an inch apart, secure 1-by-3 1/2-inch boards cut to the width of the ladder to the ladder face, so that the 3 1/2-inch face lies against the ladder frame.
Attach the ladder to the bed using two 8-hole corner brackets, placed on either side, screwing them into place using 1-inch screws.