As you may know already, my study and area of expertise is in German framing techniques, particularly in Switzerland.
In this particular style it is very common to have extreme overhangs, sometimes as much as 8'. Their reason is the same as what you desire, to protect their walls from the weather. This allows them to get away with having board siding on their houses that is 200 years old and still in fine shape, or exterior walls made of mud.
There are 2 common methods they use to accomplish this wide overhang. The first and most common is to have the tie beams which set atop the plates extend a couple of feet past the walls and then support a purlin, and have the rafters then extend another couple of feet out past this purlin, joined to it with a birdsmouth type joint. This type of roof relies on purlins to support this rafters, which reduces the horizontal sheer.
The other option they use is to mortise the main rafters into a sill or into the joists, and then have another set of rafters joint to this which extend out past at a shallower angle.
The first style genearlly has a roof pitch of about 9 or 10, while the latter has a main roof pitch of say 10 or 12.
I can supply some drawings if you dont understand what im talking about
DLB
