Building a Home Server

First off, I'm not sure if this belongs in here or not, but I couldn't think of a better place for it. I've been contemplating getting a NAS drive for the longest time so that I can have automatic backups and storing of pictures and videos. I was mostly looking into Synology drives. More recently, I thought that it might be better to just build my own home server. I don't have any experience in this, so I was thinking Windows Home Server 2011 might be a good piece of software to buy. It seems pretty straightforward in terms of setting things up and getting it to automatically backup my files on my computers at home. It seems that Plex will also be able to run just fine.

Do you guys recommend building my own server from purchased hardware (which I can do) or buying something like an HP Proliant microserver and installing WHS 2011 on that?

If I'm building it myself, what kind of hardware would you recommend? Mostly, what kind of processor would be best? I understand it doesn't need to be anything beefy, but being able to transcode my video files with ease is a must.