I think you could eliminate the double-framed roof as you show it here entirely, and accomplish essentially the same thing by having a 'double roof' as I often have seen it employed in Switzerland. You have your primary roof onto which an insulation barrier is applied. Atop that, you attach strapping screwed through the insulation which holds the roof decking or tiles or whatever you apply.

This same concept is used somewhat less often in North America.

I'll fill you in also on how this system is used today.

First of all, 'Plank and frame' or 'Bohlenwand' techniques are the inferior of the two solid wood infill techniques. The better technique is what I know as 'Fleckwand' which you should think of as a log infill. This technique descends from a hybridization of log and timber building in the sub-alpine regions on the northern verge of the Alps (in contrast to the Bohlenwand or thin plank infill which is simply a timber frame with boards inserted between the framing)

A lot of the Log infill methods actually are not infill at all, the horizontal timbers are bearing the loads and the posts simply secure their ends and create a simpler means of laying out and joining the corners. So it is really a log structure with uprights (not posts, because they don't carry any weight) Though later it evolved into timber frames with log infill.

What some manufacturers are doing today is constructing the log infill as an engineered component, a piece of insulating foam sandwiched between two layers of wood. (I am not a fan of this)

These houses have modest thermal performance without adding any insulation. Even today new houses are sometimes built with heavy log infill and no insulation added. However, when they do wish to add insulation it is applied to the inside. Americans like to have big heavy timbers seen inside the house and a nice wrap around the inside. The people along the northern edges of the Alps prefer to leave the framing exposed on the outside and apply a nice enclosure on the inside. They use generous overhangs (think like 12 feet) to keep the frame dry.

The Swiss sometimes employ a concept quite similar to what you seem to be working toward, only instead of building 2 separate heavy timber frames they construct a light frame on the inside. They don't use this frame to support anything -the loadbearing structure is all tied into the exterior frame.