Prepare the Lumber

• 1). Cut your lumber to the needed dimensions.
  
  
• 2). Sand all faces of your lumber using fine-grit sandpaper
  
  
• 3). Apply one coat of paint to all faces of your lumber.
  
  

Build the Mattress Frame

• 1). Arrange one 2 by 4 by 72 inch beam and one 2 by 4 by 39 inch beam in an "L", set so the ends of the long beams abut the faces of the short beams. Screw them in place with two wood screws per point of connection.
  
  
• 2). Repeat step one to build a second L, using the remaining 2 by 4 beams.
  
  
• 3). Arrange the two "L"s in a rectangle. Connect the corners as you did the corners of the "L's.
  
  
• 4). Set the plywood sheet on top of the rectangle. Screw in place with one screw per corner and one screw on center for each edge.
  
  

Add the Legs

• 1). Set one 4-inch by 4-inch post in the corner formed by two beams at the underside of the frame.
  
  
• 2). Screw it in place with two wood screws drilled through the plywood and into the end of the post.
  
  
• 3). Reinforce with one screw through each of the side beams and into the sides of the post.
  
  
• 4). Repeat steps two and three with the remaining three posts, setting one leg in each corner of the frame.
  
  
• 5). Lay the 72-inch plank so it connects the legs on one long side of the bed frame. Set it so that it's parallel to and halfway between the ground and the mattress platform. Screw it in place with one screw for each leg.
  
  
• 6). Lay one 30-inch plank so that it diagonally connects the 72-inch plank and the beam of the bed frame. Screw it in place with one screw at each point of connection.
  
  
• 7). Repeat with the other 30-inch plank, running this plank at the opposite angle of the first.
  
  
• 8). Lay one 36-inch plank so it connects the legs on one short end of the bed frame, set parallel to and halfway between the ground and mattress platform. Screw in place with one screw for each leg.
  
  
• 9). Repeat with the other 36-inch plank on the opposite short end.
  
  
• 10
  
  Lay one 24-inch plank so that it diagonally connects a 36-inch plank and the beam of the bed frame above. Screw in place with one screw at each point of connection.
  
  
• 11
  
  Repeat with the remaining 24-inch plank, bracing the opposite short end.
  
  

Final Steps

• 1). Apply painter's putty over the heads of the screws and any dings in the lumber. Allow to dry.
  
  
• 2). Sand off excess painter's putty and any burrs that occurred during construction.
  
  
• 3). Paint the frame. Allow to dry.
  
  
• 4). Set the frame in position. Slide the original twin frame in beneath.