Why build instead of buy complete: Save a little money. The AR-15 platform is an inexpensive weapon overall, and owning one is on-par with buying a much less versatile bolt-action rifle. So for a similar price you get additional versatility. Bolt action rifles are great for reaching out beyond 200 yards, but if the pack of wolves or wild dogs is closer, the bolt action will be a little slow. However, a new AR-15 can still be pricey. A Del-Ton Sport (http://www.del-ton.com/carbine_rifles_s/2.htm) will run you $707 in spring 2014, plus local fees, FFL fees, and shipping. My experience is that by building out an 80% lower receiver you save about $100– money you will want to spend on optics, slings, a case, and so forth. Of course, you would actually spend that money in addition to the cost of a rifle regardless.