Re: .308 cheeper to build or buy?
Question for yourself: Do you want to build a rifle because you like and REALLY want to do the work yourself, or is money the ONLY factor? If the answer is yeas to part 1 invest in the tools; minimum .308 headspace gages go no-go, the appropriate barrel nut wrench, the .308 AR receiver block, a strap wrench depending on the handguard type. Most of the other tools will be dual use for the AR build. Then go and find your parts. The key to good shooting AR is a good barrel, Free floated handguard, a quality bolt and finally a good quality trigger. From there its up to you what else you want to put into it.
If money in the sole motivation. Buy a quality DPMS, Rock River or Armalite or what ever brand you desire. Use the routes described above saving the money on taxes or dealer costs.