Instructions
Decide how much space you have available for your play fort. Remember, you need at least 6 feet around all sides of the play fort for kids to play. Choose an area of your yard that is relatively flat and visible from the windows of your house.
Buy a play fort plan or kit. If you are handy, you could also try designing your own. Make sure your play fort will meet the needs of your kids now and in the near future. If you have very young kids, keep the deck and accessories low to the ground. But remember that kids grow, so make sure you can adapt your play for older kids.
Buy the materials and accessories you need to build the play fort. If you are buying a kit, most of the wood and connectors will be included in the box. If you are using a kids playhouse plan, purchase wood that is resistant to rot. You can use cedar or treated wood. If you do use treated wood, use ACQ treated lumber instead of CCA to avoid exposing your kids to arsenic. Make sure you also purchase fasteners designed to be used with treated wood. Use 4x4 posts for the side supports, 2x6's for the joists and 1x6 decking for the floors. Use 2x4's and 2x2 posts to make the railings.
Level the ground for your play fort. If the ground is not level, your play fort will tilt. You can compensate for uneven ground by adjusting how long the supporting post are if you are building a play fort yourself.
Measure and mark the area for your play fort. Make sure the corners are square. Dig a hole for each 4x4 supporting post. Pour concrete into one hole and insert the bottom of a post. Support the post with 2x4's until the concrete has set. Use a level to make sure the post is completely straight. Repeat with every other post. If you don't want to use concrete, you can use swing set anchor stakes, but these don't hold as well.
If necessary, measure and cut any lumber. Sand off and rough edges or splinters so that your kids don't get hurt. Screw the pieces of the play fort together with the appropriate screws. Once the play fort is built. Check for any loose joints or protruding screws.