Tree houses are made from a variety of materials and no two are alike. The builder's creativity and imagination are the limitations and the main tools needed for this job. Tree houses can be made from recycled or new materials. Attaching a house to a tree may harm or even kill a tree. Scaffolding set in the ground and erected next to the tree will place the house in the branches and keep the tree from harm.
Many businesses throw out pallets. Be sure to ask permission before taking pallets in case they have other plans for them. Use four 4 by 4 corner posts concreted into the ground next to the tree to create the scaffolding frame. Attach pallets to all four sides, from bottom to top. Pallets will provide sturdy scaffolding as well as a ladder to the top. Other items may be used for corner posts, such as logs, but whatever you use, make sure they are heavy and sturdy enough to hold up a small house.
Used furniture stores sometimes throw out furniture that is not saleable. Ask permission before removing items from their dumpster. Junk yards can be treasure troves for tree house material. Dresser drawer fronts can be used for window shutters. Table tops may work well for a floor, roof and walls. If your tree house has a deck, table and chair legs can be used for railings.
Fenders, doors, hood and car roofs are all things that can be found at an auto junk yard. These items can be used to create a very interesting tree house. A car door can be used as the tree house door. Other car body parts can be used as the floors, roofs and walls. The seats can be used as furniture inside. The shell of a car can even be used as the house itself.