A floor plan is not necessary to build a tree house, especially for simple one-room designs. However, depending on the complexity and size of the tree house, pre-planning and schematics of some sort typically result in a safer, sturdier and more level house.
Platform tree houses, which do not include walls or a roof, constitute the most viable tree house to build without floor plans. For builders with good spatial planning skills, quick sketches with dimensions often provide sufficient planning for a basic tree house. For more complex designs, a floor plan or detailed step-by-step instructions and dimensions provide the simplest means to ensure a successful project.