Build Practice Mode?
How about a simple mode on Howling Abyss where you can take a champion, choose the level you're on and the 6 items you have, and practice against a friend you invite to do the same thing-- or possibly even just a random match up at level 18? I can see so many more unique builds on LCS because of this and much better strategies. We don't always make it to max build level 18 to be able to play around with builds.