NAS Server OS/Software Suggestions

I want a NAS solution to back up my PC and host media files, but prebuilt NAS solutions are incredibly expensive and underwhelming and so I'm planning to build one. Does anyone have recommendations for a NAS interface?

I'm brand new to server management and would prefer something user friendly. I have used linux mint, but currently use windows as my daily driver (planning to switch to mint soon). I'd be fine with a dedicated NAS OS or with something I could run on mint since I'm already familiar with that distro.