Use a hand saw to cut two 36-inch-long side braces and four 12-inch-long top support braces from the 2-inch by 4-inch boards.
Lay two of the 8-foot-long 4-inch by 4-inch boards next to each other on a level surface and separate the bottom of the boards until the two top boards are only touching at the inside tips (forming a V-shape) and the bottoms are approximately 4 feet, 6 inches apart. Repeat this with the other two 4-inch by 4-inch by 8-foot boards.
Set one of the 36-inch-long side braces halfway up the A-shaped legs and drill two 3/4-inch holes through each end of the brace into and through the legs with a 3/4-inch drill bit in a drill. Repeat this with the other 36-inch-long side brace on the other two legs.
Thread a 6-inch-long galvanized steel lag bolt through each of the four holes on each A-frame assembly, and secure them on the inside of the frames with a washer and nut.
Position the two A-frame sides 9 feet apart with a saw horse next to each of them.
Pull one of the legs on each of the frames up so that they rest against the saw horses with one leg flat on the ground and one leg against the saw horse.
Position the 16-foot-long 4-inch by 4-inch top beam within the V-shape on the top of the two leg frames. Center the beam so that there is an equal overhang (approximately 30-inches) on each side.
Drill two 3/4-inch holes through the two A-frame leg boards and the crossbeam. The holes should be centered and evenly spaced 1 1/2-inches from the leg apex on each side of the swing set frame.
Thread an 8-inch-long lag bolt through each of the four holes, and secure each one in place with a washer and bolt.
Drill six evenly spaced 3/4-inch holes, 1 1/2 feet apart, starting 6-inches in from the legs, through the crossbeam. These holes will hold the swings, trapeze bars or glider.
Thread a 3/4-inch-wide, 5-inch-long eye bolt through each of the holes, through the bottom of the beam, and secure them on the beam with a washer and bolt at the top of the beam. Enlist the help of a friend and stand the swing set up.
Build swings or a glider from 2-inch by 4-inch boards or a trapeze bar from a wooden dowel. Alternatively, purchase ready-made playground equipment and hang the pieces from your swing set with galvanized chain or vinyl coated chain.