I think the Lenovo Y500 is pretty sweet. Getting the model with Dual GPU. Go for it

Unfortunately, you cannot build your own laptop. Anyways, as of right now, the Lenovo Y580 seems to be the best "bang for your buck" gaming laptop. You can easily play any game to date (including Crysis 3!). If you get the cheapest version with the 1366x768 screen resolution, you will be able to crank to the max. If you get the 1080p version, you should be able to crank Battlefield 3 fully maxed out at 1080p. I was [i]almost[/i] able to on my ASUS G73SW, which had a 460M, and the Lenovo Y580 has a 660M. Going from my past gaming laptop experience (and I doubt it's changed since then), your battery will suffer. Do NOT expect 6 or more hours out of a gaming laptop. You will only 2 maybe, 3 if you're lucky, and that's on power-saving mode. And when you're playing games, MAKE SURE that the charger is plugged in, because on my G73SW when it wasn't, my video card wasn't performing to its fullest. Dunno if it's the same on the Y580 though. So again, as of right now, the Lenovo Y580 is the best bang for your buck, and I've only been reading positive reviews. Although I've never owned it, and going off of the reviews, I highly recommend it.