Thoughts about my NAS build?

I'm thinking about getting myself a NAS, I don't know whether I should get a pre-built or a custom one. It's aobut if it's worth it - getting a custom. Will that make it much cheaper with a similar performance?

So, this is what I have come up with: http://pcpartpicker.com/p/Xy9K23

And for comparison, one pre-built that costs a little bit more than my custom one (I live in Sweden, avalability may not be exactly the same as for you):

QNAP TS-269L

CPU: Intel Atom D2700 Processor 1,78 GHz.
RAM: 1 GB DDR3.
2 x 3,5"
2 x USB 3.0, 3 x USB 2.0
1 x eSATA2 x (I guess 2 ports)
Network 10/100/1000 Mbit/s (not wireless)
RAID, JBOD, RAID 0, 1
1 x 70mm fan

And the NAS doesn't need to be seriously kickass, I don't need two thousands TBs, probably just 1TB, though, I might just get 2TBs just in case.

What I wonder is, what do I win on getting the QNAP, except for size (yes, it's a little bit smaller) and having to build a PC?

Also, what do you think about using a Raspberry Pi? I have read tons about it, although I still don't know - how will it perform? I already have one, so that might be an option, right? And as I said, it doesn't need to be the best, it just needs to work fairly good and not break down because of nothing or something.