Are Custom Games hosted by you or Riot Servers?

This is a question I ask, because I see so many custom games, and you can literally make a custom game with only you in it and 9 A.I, so me thinking that would be a waste of Riot Bandwidth makes me think its hosted directly on your own machine. However, lets assume its a 10 human custom, that may not be suitable if you have bad internet...

So bottom line, does riot host all matches regardless of match-up setup?