On Wednesday, July 25, 2018 at 10:51:27 PM UTC-5, -MIKE- wrote:

First thing that jumps out to me is a four sided hip roof and pyramid
hip roof.
All the rafters would terminate near the two trunks and you could get
creative with how it all joins together at the peak.

Hmmm.... I would certainly hope that the carpenters had that skill set. I am thinking of trying to header off the common rafters someway, then creating a stable frame to hold up the hip rafters, then fitting in each jack rafter (cheek cuts on one end, bird's mouth on the other)in an unsquare and unstable roof structure. A lot of work for a tree house.

I looked at the pics and the last drawing said that there was a "preferred" direction of the rafters. Personally, I would change that. Then you could make a simple offset gable roof that used all common rafters and simply block out around the trunks. In fact, you could cut the roof closely enough around the tree trunks that you could flash the base of the penetration, then attach a counter flashing (like a storm collar) around both trees and solve the water proofing as well. By counter flashing the penetrations (trees) in that fashion they would not be compromised in a windy environment.

Robert