Build it yourself, it will not only save you money it will be of a better quality when everything all said and done. It's super easy, and all you really need is a screw driver. However be warned that HDD have spiked in price since the flood in Thailand. A 2TB Samsung F4EG used to be ~$70 just a few month ago, now however they are $160. which is a steal considering at the height of things they were ~$270.
As for HDD brand I'd personally recommend WD or Samsung. I currently have 4 WD HDDs and 6 Samsung HDDs and not a single failure between any of them.
Also RAID =/= backup