Lay out a framework of two 8-foot boards parallel to each other and spaced apart with three pieces of 44 ½-inch boards, one at each end of the 8-foot boards and one in the middle of them. Set the boards so they are resting vertically, with the 2-inch width sitting on the work surface. As the framework for the platform, the boards provide necessary structural support and a perimeter of 4 feet by 8 feet square.
Lay a 4-by-8-foot plywood sheet on top of your framework, ensuring that all edges line up evenly.
Use a power drill to screw 2-inch wood screws through the plywood and into the boards, from the top down. Space screws evenly around the entire perimeter of the plywood sheet, no more than 1 foot apart, and ensure that the boards remain flush with the plywood. Once the outer perimeter of the frame is securely attached to the plywood, screw the center board into place as well.
Turn over the platform, so the framework of 2-by-4-inch boards is showing. Place a 4-by-4-inch post vertically in each corner of the platform, flush against the 2-by-4-inch boards.
Clamp the posts into place and drill two 3/8-inch holes through both the 2-by-4-inch board and the 4-by-4-inch post as bolt holes, from one side only. For increased durability, ensure that the holes are not perfectly aligned with each other, but rather on a slight diagonal and about 1 inch apart vertically.
Bolt the 4-by-4-inch posts into place using 3/8-inch-by-6-inch graded hex bolts and nuts, tightening with two crescent wrenches. For added stability, 4-by-4-inch posts may be attached to the center of the platform, where the middle board meets the two long outer boards, as well.
Repeat Steps 1 though 6 to build a second 4-foot-by-8-foot-by-3-foot platform.
Align the two platforms upright and side by side, creating an 8-foot-by-8-foot surface.
Clamp the adjoining 8-foot boards of the platforms together from underneath. Drill two 3/8-inch holes through both boards, evenly spaced between the middle and end boards of the 2-by-4-inch framework.
Bolt the two platforms together using 3/8-inch-by-6-inch graded hex bolts and nuts, tightening with two crescent wrenches.