That is not going to work.
These open source builds are NOT for generic PC's which your intended platform (Core-i5) is.
They are for people with a Syno (or another device with very similar hardware) that are willing to invalidate their warranty and mess around with things.
They are NOT for people who want to build their own NAS on basis of a spare PC they have lying around.
It is possible to (starting with the Intel Atom version of the open-source build) modify these sources to run on generic PC hardware but that requires a good understanding of the Linux kernel and how to build your own custom kernels.
The fact that you needed to ask this question in the first place shows me that you don't have the knowledge to make an attempt at this.
If you are dead-set on building your own NAS from scratch you are better of looking at FreeNAS or OpenFiler. These are both Linux distro's specifically designed for that.