Cut the frame pieces. Saw two 1 by 6-inch by 4-foot long pieces of lumber (longer pieces) and three 1 by 6-inch by 3-foot 10 1/2-inch long pieces (shorter pieces). The plywood piece for the platform top will be a 4 by 4 foot sheet.
Lay the two longer frame pieces parallel to each other. They form two opposite sides of the platform frame. Two of the shorter lengths of lumber create the other two sides of the frame. The third shorter length of lumber creates a brace piece in the middle of the frame half way between the two shorter length sides. The three shorter lengths butt up to the sides of the longer length pieces of lumber. When completed, this frame forms a 4 by 4 foot base for the plywood top. All edges should be flush and level.
Attach the longer frame pieces to the shorter length pieces using drywall screws. For stability, use three screws in each spot where a longer piece and shorter piece come together to make a joint.
Place the plywood top on the frame. Insert four drywall screws through the plywood along each of the four frame edges and down the center brace frame piece. The frame and top should be solid, level and approximately six inches high.
Assemble the platform steps by staggering their placement as they rise to the main platform. Place the first platform step on the ground. Place the second platform step on top of the first platform, 14 inches back from the front edge of the platform. This creates a tread (or horizontal surface for the foot) to step on. Draw a line along the edge of this tread. Remove the second platform.
Attach a 2-foot long strip of 2 by 4-inch lumber along this guideline on the first platform. Place the second platform back on top of the first platform. The 2 by 4-inch strip fits against the inside front of the second platform frame. Place the second platform back on the first platform step.
Cut step legs. Measure the distance from the ground to the top of the second platform step frame. Cut two pieces of 2 by 4-inch lumber to that measurement. You are creating legs for the end of the second platform that is not supported by the first platform. Fit the legs inside each unsupported end corner of the second platform. Secure legs using drywall screws. Repeat steps 2 and 3 for each of the remaining platform steps, making the adjustment in the leg length for each rising platform step.
Check all steps for stability.