I just built my own, and I wanted an 8-Bay so I could have 4 for RAID and another 4 as backup to the RAID array.
Unfortunately there is not a huge choice of 8-Bay NAS cases with hot swappable cages. The good news is there are a few such NAS cases like the Silverstone DS380 and U-Nas NSC-800. Grab one of these with a mini-ITX board, an i3 or Pentium, 4-8 GB of RAM, a small 300w PSU, an HBA, and several WD Reds' and you're good to go!
If you do still want to mess with the hassle and rather just go with a pre-built appliance route, I recommend the ASUSTOR AS-608T or QNAP TS-869 or Synology DS1813.
Also I decided to go with Software RAID, because onboard motherboard hardware RAID or buying a cheap RAID card have a high chance to fail on you within 5 years! Try ZFS if you're adventurous, or WHS if you're not into Linux.