It's not all that difficult to build an AR as long as you have the proper tools. For a noob, it might be a good idea to just look at the different forums pic threads (here, AR15.com, 68forums, etc...) to get an idea of what you want. Once you've done that, look at the different websites (midwayUSA, Cheaper Than Dirt, BCM, etc..) and start pricing stuff out. I'm not all that experienced myself...been shooting ARs for 12yrs and just got my first one last month.
The one thing I found price-wise, it was cheaper to buy both a complete lower, then buy the stock kit I wanted, and then bought the upper and other accessories. For a complete lower, you can't go wrong with an Aero Precision. If you are anyway near Lakewood, Wa you can get a complete lower from Surplus Ammo and Arms with the stock for $180 and without the stock for $130. For the upper, you have many places to choose from-RRA, Stag, DPMS, Noveske, Colt, Armalite, and the list goes on.
Good luck and happy shooting.