Determine the height of your bed by placing a tape measure against the floor and extending it upward. Note the total height of the frame, box spring and mattress. Do not include the bedding.
Measure the thickness of the crib mattress you plan to use in the bedside crib. Subtract this measurement from the height of your bed to determine the height you need the bedside crib frame to be.
Determine the width and length of the crib mattress. Sketch a diagram that includes a flat plywood surface that is the same size as the mattress, and legs that are the height of the crib frame.
Cut plywood with a circular saw to form the crib's base plate and three sides. Leave one of the longer sides open for access to your baby from your bed. For safety, sand down any rough edges before assembly.
Assemble the crib frame by screwing through the bottom of the base plate into the three plywood sides. Place additional screws into the sides where they meet to form corners.
Cut lumber to length with a circular saw to form the crib legs. Screw through the top of the base plate near each of its four corners and down into the legs below. Screw additional lumber horizontally between the legs to form stretchers that give the crib added stability.
Paint or stain the assembled wood frame. Insert the mattress and bedding once the finish is dry.