Hey guys and gals! This is my first instructable so it might be kind of crappy but, oh well :)
I just thought about making this right before I finished building my fort so there might not be that many pictures, and its kind of messy. Well hope you enjoy it :)

Step 1: Finding the Spot

The place I built mine was in a triangle of trees. So I had a triangular tower.
But a square tower would work also.

NOTICE:
This instructible is for a triangular tree fort so if you want a square then think about how to make a square using this.

Step 2: Materials

Materials

Another person ( to hold up the base and support boards while you nail/ screw them in)
Saw ( I used a regular hand saw but any other saw would probably work to)
Cordless drill
Level
Ladder
Hammer
measuring tape
8/10 large foundation nails
1 or 2 big boxes of screws
2x4's for the base and support beam ( length and amount depend on the size of your tower)

Step 3: Building It Part 1 the Base

1. So first, have your friend hold up one of the main supports while you nail two foundation nails into each tree.
2. Now, once they are in properly do it again, but this time use the level to make sure that they are in the same spot
3. Repeat step two until you have they main outline of the square/ triangle.
4. This is where you use the ladder. You set the ladder up so that you can climb up to the frame easily.( unless, of course it is close to the ground)
5. Now you climb up the ladder and place down the first board. Make sure it is the right size before you screw it in.
6. Continue step five until you have the main platform that you can fully walk on.

TIME FOR PART TWO

Step 4: Building It Part 2 the Walls

1. Now, place the ladder on one side of the platform that you are not going to get up on. ( see pictures above )
2. Have your friend go on top of the platform and hold up the 2x4 while you screw it in with a two long screws on each end.
3. Do step two again, but on a different side.
4. Now, there should be two railings and one open side.
5. Now here is the tricky part. see drawing above. ( the dots are screws And the boards are 2x4s)
6. Next you move the ladder to the open gap between the tree and the half railing.
7. And voila you got a tree fort.

Step 5: Upgrades

Now is the fun part. Now that you have the main thing done, you can customise it! You could attach a pulley to a small tree limb, feed a rope through it, and tie it to a bucket, and you have a stuff elevator! You can put a roof walls windows and a door on it, then you have an actual tree house! You could put chairs, tables, toys, coolers with food and purple drank ( as long as you take them back inside in a day or two), the possibilities are endless. Just make sure you have fun doing it. If not than tear it down and rebuild it.

Step 6: The Finished Product

Now you have a cool tree fort! It could be a sniper tower for airsoft or paintball, your secret hideout, your clubhouse, anything you want it to be. Well have fun! :)