It only took me 4 hours, from opening the boxes to an installed OS. Apparently though, Dell's production staff have to be able to assemble a PC, much the same as the one I built (ie, the XPS') in less than an hour. Bit of useless information for ya
Definitely recommended to build vs buy, if you do it right you'll actually save money versus buying a ready-built (i.e., mine was €750, and an XPS that I was looking at which actually has far less power was €1200. Plus Dell are known to use inferior manufacturers). Plus there's the upgradability, and knowing what exactly is in the PC (kind of like organic foods lol). I wouldn't worry too much about how fragile they are, I dropped my CPU taking it out of the box 4 feet onto the motherboard below, and everything still works perfect. A good guide I followed is
this one, it's well up to date with all the latest hardware, easy to follow, far more extensive than most other guides, and if you end up stuck, you can leave a comment on a particular step and someone will help you
To order parts I reccomend
www.hardwareversand.de, despite what anyone else says about them. My stuff came from Germany within a week of ordering and sending the payment, and they have
the cheapest prices you'll find...
For £400 you could get the same setup that I have (probably even better, prices are dropping all the time), and I get 100-200 FPS with dual screen. The only time I saw it less than 100 FPS was playing bump and jump with 18 players in front of me on a full layout
BTW, all the necessary wires and cables come with the motherboard