I've done this a half a dozen times when you include the gamer boxes I've built for myself and friends going back to the Counter-Strike Beta days.
If your really going to build your own box, spend the bulk of your coin on the Video Card. Make sure you get a Mobo that will be able to support an upgrade in the video department at least once about 18 months down the road, and feed it as much RAM as possible.
Be careful when pricing out the components to include tax (If they are in california, you pay it) and shipping. If you find a place that has competative prices on multiple components, you will save on shipping by grabbing several chunks of the box from there.
$1000 is probably enough to build a decent "Slay Station" but if you could somehow squeeze yourself another $500, that box will scream for at least 12 to 18 months.
One of the major reasons I stopped gaming via PC was the fact that it seemed like I was pouring $500 to upgrade the damn thing a year after I built it for the new game set coming out that fall, and building a new box every 2 years, and that was just to be able to stay on top of the video requirements. I had to have as many FPS as possible or I was just going to get smoked.