The classic tree fort can range from a simple wooden platform perched among the branches to a two-story marvel bigger than some homes. Depending on what you have in mind, you may be able to construct a tree fort using scraps of lumber, or you may need to hire a structural engineer to ensure your design will hold if you have something more elaborate in mind. No matter what type of tree house you build, a backyard fort provides plenty of lessons for kids, from working with their hands and safe tool use, to respecting and appreciating nature. If you have older kids, you can also incorporate them into the planning, teaching them how to use math, science and engineering to design the tree fort of their dreams. When you're ready to build, choose flexible supports and floating brackets to allow the tree to sway safely in the wind [source: The Family Handyman].
No tree? No problem. Create the same effect by constructing your fort on a simple raised platform in the yard, with a ladder or rope ladder to provide access to the fort itself.