We recently designed and built a private tree house and play area near Winchester! The area includes a speedy zip-wire (which only hindered subsequent productivity a little bit…), a large cargo net and a tree house 6ft above ground.
The tree house has a reciprocated roof, whereby each rafter supports the next. It’s a brilliant design dating to the twelfth century and we’re now using it for our own round house designs. See the picture below for an illustration:
