Just don't fall into the trap of thinking that you will necessarily get better value for money by building it yourself. The reason I say this is, I built my AR-15 from a kit - I bought a stripped lower, a kit containing a pre-assembled upper and the remaining parts to complete the lower. All this came to a reasonable price. But from the very beginning, the trigger malfunctioned. The lower I fitted it to was a good quality RRA. Everything fitted fine, but the hammer would sometimes drop when the trigger was released, which is dangerous and could cause legal problems too. Besides all that, the trigger was terrible - heavy and creepy.
Anyway, I sent the bad trigger parts back to the retailer and replaced it with a drop in trigger, which cost $250. So now I have a rifle that is perhaps as good as a $1000 factory rifle, but it has pretty much cost me $1000 plus a lot of hassle. Not to mention is probably has poorer resale value due to the lack of a brand name.
I am sure that more experienced AR builders would have more success, but for a first AR, I'd recommend buying a factory rifle.