Lay the 5-foot boards on their 1-inch widths so that they run parallel to one another and are spaced 3 feet apart.
Position a 38-inch board at each end of the 5-foot boards to form a rectangle. Align the boards so that the ends of the 5-foot boards are set against the faces of the 38-inch boards.
Drill two screws through each of the 38-inch boards and into the ends of the 5-foot boards at each corner to create a rectangular frame.
Stand a 6-inch stake upright in each inside corner of the frame. There should be a 2-inch gap between the top of the stakes and the upper edge of the frame.
Drill screws through the frame and into the stakes to secure them to the corners.
Set the sheet of plywood over the frame and allow it to slip between the frame boards. The plywood will come to rest on the stakes set in the corners.
Set screws every 6 inches along the outside of the frame to secure the plywood to the frame.
Stand the four posts upright and position one post into the inside of each corner over the plywood.
Drill holes through the frame and posts along the frame's sides where the posts and framework touch.
Slip a lag bolt through each drilled hole and secure the accompanying nut to attach the posts to the frame.
Flip the table right side up and rest it on the post legs.
Drill eight to nine scattered ½-inch holes into the plywood; these will serve as drainage holes.
Spread a piece of landscaping fabric over the plywood and use a staple gun to attach the fabric to the edge of the frame in 1-foot intervals.
Place the garden table into its new location.