The first server I ever built was a cheap media server. I gutted a broken Nintendo and modified the case to fit a mini ITX motherboard. I installed an AMD A-12 processor, 8 gigs of DDR3 ram, and  a 256 gig SSD drive. The original OS I installed was Linux Mint but I switched to Ubuntu for no particular reason. I mounted an 8TB external HDD for storage and shared it over my network. And finally, I set up Plex to be used as my media server.