I think it's wise to pass on that one. The polymer lower and commercial stock/buffer tube are indicators of corners cut to meet a certain price point. Besides, $800-1000 can get you a really good AR that you'll be proud of and can trust if that very bad day ever comes. You'll see the names PSA, BCM, Colt and S&W a lot when good ARs are discussed. There are others of course. PSA tends to be the bargain these days.
Now there's nothing wrong with a custom build but I'd say do it yourself after reading the above stickys. Many of us here have done that and I can't remember anyone who was sorry they did, providing "due diligence" was done research-wise. (Most builds actually are assembling a stripped lower then buying a good upper receiver group.)
Anyway, lots of stickys and other informative threads here, take your time and enjoy!
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek