For a child, there's nothing more magical than a treehouse. There's nothing more terrifying as a parent, however, than the prospect of building one. These treehouse design ideas and prefab options range from extremely simple to outrageously cool and complex, depending on how well you can work a hammer (plus a few more tools and supplies). But don't worry-there are plenty of treehouse design ideas to inspire everyone's inner child. Plus, they're actually pretty enough to keep up in the backyard long after the kids outgrow them (one of our treehouse ideas, for example, is a stylish, dreamy guesthouse escape).