I've seen it done, regarding the octagonal plan.

And roofs can be done any way you want, the concept of this framing is that the framing of the roof and the walls are pretty much independent of each other.

And I'm a product of Bern, so I tend to be biased to the region All those things you mention, ya they're kind of a big deal there! You buy me a plane ticket, I'll give you a personal tour! I know all the best spots...

As for framing octagonal designs, it's actually done quite frequently (think castles) Usually, they accomplish this by having a post in the corner that is cut with specially angled faces. But I rather like the idea you show in your other thread of just putting one post either side of the corner and letting the trim job do the rest (though this may be hard if you're doing an infill)

I'll look through my extensive photo gallery (think like 5k pictures) to see if I can find you some octagons.

But regarding super efficient, ya I'm swiss so... I tend to be preoccupied with the concept in a way that is probably annoying to everyone else (why can't you just let things be -because I'm Swiss, dangit!)