A home build pc won't run better then a pc from store if they have the same specs.
If you really want to try it.
Just do it.
But make shure that it is a good system, don't rush on choosing parts.
Make shure that every component will work as it should work.
On my last pc, i bought a fast graphic card, but a not verry fast processor. (singel core)
Result: Graphics where awfull, textures where shown all wrong.
And I had to buy a new processor (dual core) wich costed me €140 just to make the system run good.
And that is why I will never build my own pc again.
If you buy one from dell or hp, all the components work good, they are tuned on eachother and the system works stable.