No, not common at all. The thing that dictates the design is solar panels. I'm by no means a tree huger, I just like being off the grid, or independent of it.
Being a solar thing, the slope faces due south, and the wind mostly comes from the west, south/west. So I may add some cross bracing. But considering the history of this area, I really don't think its needed. Architecturally, the lean of the roof has no effect beyond wind loading as you mentioned. All loads are still transferred straight down. So as long as you have enough structure to carry the load, everything's peachy. The only thing I worry about with this design is the stiffness of the center of the roof. I keep doubling and tripling up the roof and cross joist there. I always over build everything, so I'm sure that before this is done, the center will be strong enough to park the vette on....
I think half the reason I posted this was to get some of you interested in google sketchup. It's free and there are many many tutorials on it on youtube....
As you can tell from this pic, you can lay out your whole property in as much detail as you like. Great for finding underground pipe n such later on, or just experimenting with additions n what not....