If I was building a box specifically as a server, to store files I considered precious and couldn't just re-download from somewhere, I would want data protection, at least 2 drives mirrored. I doubt Roon needs high bandwidth so SATA SSDs are likely more than enough. For the boot / Roon drive if you use an NVME drive certainly don't get PCI gen 4 as they all run hot.
If you want 8TB of storage (and don't want to pay for a full drive 8TB+N array of SSD, which isn't that cheap) that puts you on spinning rust though, and HDDs aren't silent, and that also puts you in actual NAS territory. I don't use Roon so I can't speak to CPU requirements, but the Raspberry Pi players all do DSP etc with ease and I'm pretty sure LMS can run on a pocket calculator, it's not like you're transcoding video. Roon's
page on NAS is like 5 years old and a modern Celeron blows the doors off a 5-year old i3 so I'm not really sure what their actual minimum hardware is.