The design above is by Truitt Foug Architects. I love the modern shape and chunky structure! I can imagine kids climbing the walls of this one! If you look closely you can see a second floor or loft area. It appears to be 6x6's (I'm guessing size) resting on the horizontals that make up the walls. Sometimes the most basic straightforward designs are the best. Also, notice that the entire play space was pulled off using only one material. Ok, one material and fasteners, but still.
It still amazes me that there is such variety in playhouse design. It's great to go from looking at a highly ornate playhouse of the past to minimalist modern structure like this one!