Get a fractal case, go to pcpartpicker for the rest… Get a gold PSU… Be sure to check on getting a motherboard-cpu combo that supports ECC RAM… Install a linux distro with proper support for zfs (e.g. I wouldn’t recommend Arch), perhaps TrueNAS Scale. Done :)
Any PC building guide, use a case with enough 3.5" bays and a mainboard with plenty of SATA and M.2 ports (if you want SSD csche).
After that it gets more specialized.
Get a fractal case, go to pcpartpicker for the rest… Get a gold PSU… Be sure to check on getting a motherboard-cpu combo that supports ECC RAM… Install a linux distro with proper support for zfs (e.g. I wouldn’t recommend Arch), perhaps TrueNAS Scale. Done :)