It all boils down to what you want to spend and what type of AR you want. If you know what types of specific parts you want in each section or your rifle (like say, a generic BCG vs milspec vs nickel boron), you'll be best served building your own. But if you haven't yet discovered exactly what you want, your only real gain in building will be knowledge and experience.
As far as builds go, I think $800-1000 can go a long way on a Spike's build through JoeBob's
. And in the $900-1300 range, it's tough to beat BCM
Here's what I think is a quality starter build that will treat you right:
Spikes MOE, MilSpec mid-length (JoeBob's)
Spikes Stripped lower, Spikes LPK: $150
Spikes ML 16" MOE complete upper: $510
(add $100-150 for more elaborate handguard)
Magpul MOE stock, grip, MBUIS: $150
And you've got almost $200 for extras, upgrades, unforeseen expenses before you reach the $1000 mark. But some of this stuff requires waiting for it to come in stock and quickly snapping it up before someone else does.