I decided I wanted to build my own server when I was about 12. I was looking through a PC magazine and saw an article about using a Raspberry Pi as a cheap home server. Before that point I had never actually realized you could actually simply set up your own server and host your stuff on it, so I decided then I wanted to make my own so I could host my website myself instead of relying on MTS's limited 15MB personal hosting service (which they're actually taking offline June 1, 2016).
I soon went onto ebay to look for cheap parts I could use to build a system and found a great deal for a guy who was auctioning off an AMD Athlon XP motherboard with 2GB RAM and a bunch of extra parts. I ended up winning this auction and used the parts to build myself a server with a free case I picked up from my friend's dad.
After getting the system built I found a tutorial online on how to set up a web server because I had never used Linux or anything like it before and eventually got everything working.