Well, it at least sounds like the concept is plausible; not having a great handle on roof design loads nor material properties at this stage in my 'training,' I wasn't sure if I was asking for the moon or a moon-pie.

"This is a complex and deep "rabbit hole" we are entering...It is so nebulous to approach without a "focal point" design as to be inhibitive without some form of goal or context in understanding what might be the possible target..If perhaps you have some more specific ideas or goals, perhaps then we could explore more specifics design parameters and then just begin to explore what might be possible..."
I kind of figured as much. I am trying to play my design a bit close to the vest at this point, since it is more theoretical than modeled in CAD at this time*, and since I'm leery of trying to focus on too many design aspects at once early on (though I do understand how they necessarily rely on each other)

Here is the summary, of the roof at least (my other thread describes the wall somewhat)
-Octagonal floorplan, roughly 40ft diameter (~16ft walls)
-Double-layer roof; exposed reciprocal truss inside, more 'normal' peaked/hipped roof outside
-Two large column posts (forget the architectural term for columns spanning multiple floors) at the center of the floorplan help support/stabilize the reciprocal ring
-Exterior roof rafters cantilever at least 4ft past walls to shade a narrow walkway
-Low roof pitch (20deg off horizontal is my starting guess) steel-cladded

The reciprocal internal roof truss is somewhat self-explanatory, but the exterior is giving me designer's block. I'm thinking something like this, only with three triangular 'facets' on the ends of the peak line for the octagonal planform; the 'broad' faces on the front/back would be rectangular, with a peaked vestibule jutting out over the front door.

It turns out it's really hard to make an octagonal roof look attractive, without a lantern or cupola at the middle, and not have it be a cone. Or have tons of up/down peaks, valleys, or dormers, and their associated leak liability. A real shame, since the faceted exterior walls always look attractive. I get the impression it must have been a constant vexation for Thomas Jefferson, & probably Da Vinci too, who apparently were quite taken with the concept themselves.

TCB

*I model aircraft structures daily, but houses are 'different,' so setting up the assembly structure, constraining design geometry, and the general order of operations one uses to efficiently approach such a big project aren't quite online yet