At 14, I designed and built my tree house.  Secured in my rock climbing harness, and using ropes, pulleys and buckets, I hauled all the materials and tools to my building spot 50 feet up in the tallest pine tree in my backyard.  The floor plan is a triangular hexagon that surrounds the tree.  I prefabricated the frame on the ground.  It is so precise that there is not a single gap at any corner or joist.  I framed my own hinged windows and cut them from Lexan.