Forgot to mention. Building AR's is a lot of fun and a great way to build them exactly how you want them to be. We've built a bunch.
I would recommend buying a complete rifle/carbine as your first one. Learn the ins and outs out the platform them build as many as you can.
Another way to go is to buy a complete lower (from a good company) and then buy a complete upper (from a good company). If you go this way you'll save about 11% on the overall price because you don't have to pay the 11% federal complete gun excise tax. However, some manufactures don't have warranties on non-complete guns so you'll have to check into that.
Good luck, NYH1.