$900 is quite cheap for a gaming PC these days. What did you want to install?
If you mean as far as hardware goes, I can't remember much of the names now. GTX force 300 or something along those lines for graphics card, I was going to have at least 16GB of RAM, as well as either Intel i5 or something from AMD whose name I forget but from what I had read it was on par with the i5 and a little bit cheaper too iirc. I looked at this site and was going to go for something in the superb-excellent range since it would be my first and I'm not the most experienced when it comes to building. I would also buy all the parts before getting a case if I stretched it out over a few months and make sure the case would be big enough if I needed to add anything or replace a piece with something bigger.