I really wish this had been posted before we built. Our original plan had been to raise the roof timbers using a sheerlegs mounted on the first (second in American English) floor. When we lifted the sheerlegs in place and put the first piece under tension, the frame started to rack and we had to rapidly change plan. At the time my wife was concerned that the structure would never be rigid, but now that it's sheathed it's solid as a rock. A few nerve-wracking moments though.

Presumably the inclusion of more uprights and bracing elements (as in "traditional" European styles... think English Tudor, French Colombage etc) would lead to a stiffer frame before sheathing. Certainly the French carpenters that looked at my timber-framing books were concerned that there weren't enough bracing elements in the roofs.