I built my Roon server using a NUC8i7BEH with 8GB RAM and 128GB PCIe SSD.
After using it for a couple months, I decided to get an Akasa Turing fanless case so that I could move the server close to my equipment in my listening room. At the same time, I increased the RAM to 16GB, and integrated a 1TB Samsung 860 SSD into the case for my music library. Previously, I was using a USB connected hard drive for the library.
It has been working very well since I put it together six months ago. It got fairly warm when I moved the library to the SSD and I had to re-index everything, but since then it has run cool even when running multiple zones and doing some modest DSP work (upsampling and EQ).
I'm sure my configuration is over-provisioned for what I am using it for, but it sounds great, and still cost me under $1000 with all the bells and whistles.
I currently have about 4200 albums (37,000 tracks) in my library, but I still have 92% space available on the the 128GB drive. It's hard for me to imagine a library big enough to need more than the 128GB M2 drive. On the other hand, it's not that expensive to go to a larger drive.
I've recently purchased a linear power supply to use with the NUC, but I haven't had a chance to hook it up yet. I'm going to use it for a DIY amp project to do some transistor matching on a bunch of power FETs. Once that's done (hopefully this weekend), I'll relegate it to Roon Server duty.