We ordered all the exterior framing lumber for the barndo a few weeks ago while lumber prices were low-ish. The price was nearly 40% less than when we were originally quoted. Why framing lumber on a barndo? This construction relies on the steel trusses and sheeting for a majority of the build, but uses wood girts and purlins for the remainder. 

There are lots of advantages to this technique. Since the interior will be framed anyway, the 2x6 purlins and girts will contain the insulation we need to have. The ceiling will have 6" of closed cell foam for R40, and the sides about 2" of closed cell foam followed by standard fiberglass bat insulation. The wood also creates a thermal break for the external steel sheet metal that will not as readily transfer cold to the framing, thus reducing the chance for condensation. 

There are disadvantages to this construction, in that the lumber must be straight and not curved, where metal purlins and girts are not prone to curving.