This treehouse design comes from the family fun website and for any more information on how to build it, and for more pictures, please go to http://familyfun.go.com/crafts/make-a-treehouse-1024899/. This link can also lead you to the templates which will also help you to complete your treehouse.
The materials to build this are cheap if you don't already have them. They are just cardboard, paper towel tubes, any glue (I found that hot glue works best), and painting supplies. Green paint would come in handy for leaves and the canopy. I recommend using sturdy cardboard to make your treehouse more durable and less likely to be destroyed by kids!
Pictured above is my treehouse with my little brothers favorite action figures, Playmobil. Playmobil "people" fit through the slides easily and can also come in and out of the doors with ease. Also, Playmobil characters are cheap to get, so they make great residents for your child's treehouse.
Building this treehouse will not help you to expand your creativity by making a beautiful action figure/doll treehouse, it will also help you to go green by reusing cardboard that would usually be thrown out and most likely thrown in a landfill. Whether lego men, barbie dolls, or playmobil figures are living in it, I know that this cardboard tree will bring a smile to your child's face and I guarantee that they will have a blast with it! Enjoy!