I found a cool tutorial here and then I made changes to make it my own.
Because I have a boy, I figured it needed to be sturdier than the one dowel rod through the center, so I added two dowel rods along the sides.
All the holes lined up, but when I added all the dowel rods, one leg would not touch the ground. I pouted for a day and then bought four more "legs" and started over. The same thing happened. I was at a loss and without my Dad or Grandpa around to tell me what I am doing wrong, I had to do some major problem solving that lead to the front legs being shorter than the back. For some reason this worked and it doesn't wobble anymore.
I sewed the fabric where it would slide over all the dowel rods. It can only be removed by taking the whole fort apart, but it is doable in the event it needs to go in the wash.
I also added a solid back and a front flap so he could be enclosed and have the privacy a clubhouse would give him.