Eddie, thanks for the comments. I do have a written file to go with the photos, and have communicated it to the GC. Your suggestion to get something in writing from him is a good one, and I'll start on that today.
I have contacted a local attorney and he has suggested that there isn't really anything to do until the lien is actually filed, and if the GC does post a bond, that is the best initial remedy. Then the course of action is to make sure the bond and final outcome are recorded as to the property. I have another certified letter sitting at the Post Office which I'll pick-up today, probably the actual lien notice

.
I do have the withheld payment of $6,500 which is probably enough to make it right, but it certainly isn't enough if the legal side gets ugly. I intentionally hired a turnkey GC, one that provides the materials and labor, and even does their own manufacturing and design of many items. They are located on the other side of the Rocky Mountains, outside of Denver, and I'm on the western slope about 250 miles away. In our area, all of the contractors have a poor reputation for deadlines, quality of work and business principles. I'm counting on the business principles of the GC in this case, but I'll prepare to go on the offensive if needed.
Robert, the rough framing is probably the best part of the barn! It is visible on the inside, and the GC and I inspected it. It looks pretty good. I was a superintendent for US Home Corp. for a few years in a prior life and built about 150 tract homes so I learned a little about checking subs work. I was able to inspect the framing as it went up and found things to be square and I verified the level of the base and top plate with my own builders level and laser. The trusses were certified and set well. The one thing the sub seemed to know was framing. He set the building pretty well, he just didn't know much about the sheeting and was sloppy as it got closer to completion.
I have signed and engineered plans, the County looked at what I was doing and said there was no need for a permit or inspections since it was an ag project. I'm very comfortable with the structural aspects of the design and build, especially since I was actively involved in the post setting and initial framing stages.
My biggest concern is, as Eddie pointed out, the potential future ramifications of the lien. I'll have to stay on top of that one.
Thanks to all for the tips and suggestions.