Here is the cargo net, shown at right. I bought it pre-made through an Ebay seller for about $40. It is attached to the top 4x4 with 4 galvanized steel eye-bolts, washers and nuts. I drilled 4 holes through the bottom 2x6 along the ground, and tied the loose ends of the cargo net in knots and through the holes at the bottom.
One of my favorite parts of building was adding the vertical side rails and decking, because the lumber was a beautiful, smooth redwood. I also added a ladder made of pressure treated 2x4s on the bottom right side to get up into the fort. All the decking was put together with square-bit, red decking screws from Home Depot. (The square drill bits last longer and don't strip as easily as phillip head screws). Next it was time for sanding and staining the wood with a dark brown combination stain/protectant. Pressure treated wood does not technically need to be stained, but it will turn a greenish-brown-gray if left untreated. The redwood is soft and needed to be stained to protect it from sun, wind, and water.
Atop the upper horizontal 2x4s and 4x4, I added more horizontal 2x4 beams and a simple upside down U-shape frame to hold a canopy. I used deck screws to attach it, and added small blocks of wood to give it extra support where needed.
The next step was constructing a simple A frame, made of 3 pressure-treated 4x4s, and a 2x4 brace across the middle of the A-frame. The 3 pieces are connected on the top with 2 special swing-set metal brackets (one on each side), purchased from Amazon.com for about $10 each. It made connecting the pieces very easy, and sturdy.
I ordered a green tarp for the top canopy from a tarp supply company online for about $40. They come pre-made for playgrounds, but I saved a lot and chose my own color and size this way. It is a 4x6' with grommets, so I just bolted it down to the frame I had built on top of the fort.
I built the ramp ladder, at left, from 2x4 pressure treated lumber, and 2x6 redwood for the slats. The blue and white rope was purchased from Home Depot by the foot, and I added knots to make holding on easier.
Finally, I added 4 yellow plastic coated playground handles, a swinging trapeze, and a yellow heavy-duty playground swing from various online sites. At last, it was finished!
It has provided endless hours of fun and exercise for the kids and their friends, at a fraction of the cost that I would have spent on a new, pre-built set. All in all, I spent about $700 on the materials.