First of all, your comments in the email to me with the picture says the rafter sits on a post. I'm sorry but the rafter sits on a tie beam, over a post. There is quite a difference. What really peaked my interest was the fact that you said a rafter sat on a post. In colonial America there were no rafters sitting on posts, at least none that I've ever heard of. Rafters either sat on plates, as in common rafter roof systems or rafters sat on ties such as this.
This tie and rafter combination may make the roof assembly a truss. It's hard to tell without further pictures.
It is possible that the walls were raised and then the ties were lowered onto the posts, and then the rafters set into the tie. Or with gin poles it may have been raised as a truss and set on whole. It's hard to tell without further pictures or details.
