Building a Custom gaming PC?

Im looking into getting some sort of gaming PC and I need some advice. I really like the alien wares, but it seems everyone finds them to be rubbish and overpriced. Is this true or is it just something a kind of elitist says? I also hear a lot of talk about building a custom PC, but is this a truly viable option? And is it really all that cheaper compared to simply buying a prebuilt alien ware? You see, I have never put together a computer before, so obviously I wouldn't know what I was doing when I tried to build one. How hard is it and how long did it take for you to build your first PC? Is there anywhere that I could possibly find a guide? So, what do you think? Try and build my own or buy an alien ware?