Hi everyone ! 
I'm new on this forum and I would like to show you my NAS build ;).
Used parts:
- Motherboard: MSI A88XM-E35 V2
- Processor: AMD A6-6420K 4.0 GHz, 2 cores
- RAM: GOODRAM 2x2GB 1600 MHz CL11
- PSU: Corsair VS450
- Case: SilentiumPC Brutus 430 Pure Black with 2x SilenciumPC 120 Fans
- SSD for system: Transcend 32 GB on PCI-E Card
Additionally:
- 4x hot swaps for HDDs
- DVB-T PCI Card
- Second TP-Link LAN Port
My goal was to create NAS which allow to fast access to HDDs and change them if necessary without open case wall. I had hot swaps in another old ATX case but I had a problem with temperatures when PSU was on the top - 50-60°C on HDDs. I bought case with psu on the bottom. Now I have two 12cm fans. One on the top from case front and another on the back. I had to change a place for one of the fans because back fan takes air from hole on the top, not from HDDs and the temperature was rising on them. Now, the temperatures oscillate between 30-40 °C after few hours. Fans are quiet and hot swap have silencers. Somethimes I forget that NAS is powered on ;). Additionally I tried to lay the wires in case to allow maximum air flow from HDDs.
I used Flash M.2 for system because I wanted to use a small storage for system without waste disk space on for example normal HDD.
DVB-T card is using for record TV programs.
Second LAN port is my whim ;). I wanted to have another port for VM's and redundant connection.
In the future I would like to buy 4 WD RED's to make RAID5 and 2.5'' hot swap to copy data from small HDD's. At now I treat this build as a finished base for local storage ;).
At the end I want to explain why NAS was called "Optimus Prime". When I saw the case first time I thank the front looks like optimus prime's face from cartoon ;).
That's all
Enjoy!