What website has plans for a cool child's playhouse or "fort"? - playhouse building plans

I had to build a dollhouse or "strong" for many years, my son, 7 A tree house would be great, but our garden is not a tree - I have to build something on the ground. Someone please direct me to a site that has some fun plans for a theater? I want to build something myself and am looking for models to build one that is two levels and sure to be. Thanks