Drill three holes evenly spaced into the lip of the shed about one inch below the door. Use a metal bit if it is a metal shed. Make the holes slightly smaller in diameter than the through bolts.
Measure the 2-by-4 to a length the width of the door. Line it up with the holes you have drilled. Mark places to drill the lumber that correspond with the drilled holes in the shed lip. Drill holes into the 2-by-4 at these three points. Attach the 2-by-4 to the shed floor with the through bolts and tighten them with the wrench.
Measure the 4-by-4s. Use one 4-by-4 for each two feet of width at the door opening, plus one. If the door is less than two feet, use two 4-by-4s. Measure them to be 12 inches long for each three inches of height from the ground to the doorway. The length of the 4-by-4s determines the steepness of the slope. Cut the 4x4s with the circular saw.
Lay the 4-by-4s lengthwise on to the lip of the shed. Mark the place where they meet the ground at the other end. Dig a three-inch trench at this spot. Make it as long as the door is wide. It will anchor the lumber at that end. Cut the end of each length of lumber at a 45 degree angle with the circular saw. This end of the lumber will rest in the trench.
Cut a notch in the other end of each piece. To do this, measure two inches back and 1/2 inch down at the end of each length of lumber. Draw a line with the pencil to mark the measurement. Cut out the inside of the measured notch with the saw. This will give you a notch that will fit over the 2-by-4 that is bolted to the lip of the shed.
Nail the 4-by-4s into place. Measure and cut the plywood to lay over the 4-by-4s and nail it down. Place the nails at 6-inch intervals down the length of the 4-by-4s.