Well if you buy everything individually... there are a couple things you need to be prepared for.
First, you're going to have to put the stuff together. RJtech rated the Z70V as a hard level barebones to put together... so you need to know your way around things and be brave.
Second, I'm not sure what support is going to be like if you build one for yourself. At least if you buy everything from a reseller (in this case ISTNC (good choice

)) you'll have someone reliable to go to if/when something bad happens. If you do take the barebones route, be ready to deal with manufactures like Seagate (or where ever you bought your components from).
For me... it just wasn't worth the hassle for me to build it. I mean... the only things you can really buy separate are ram, proc, and wireless (optical drive has to be with the unit because the face plate needs to be stock). So how much money would you really be saving? Is it worth all that effort to save a little bit of money and loose someone to fall back on? I didn't think so.... so that’s why I just bought a built system from them. Turned out great.