Add an option to link our item sets to runes and masteries for each champion.
Also, even if we are actually able to change our items sets when ingame, add another option to the champion select (Runes | Masteries | Item set). Since almost every champion can have more than 1 build (which can work better or worse, it depends of our criteria), it wouldn't hurt anyone. I guess.
Plus, in my opinion, I'd make more wider the block where we choose the items (still talking about "Item sets" tab). It is too small for me, and after making some sets, it ends up to be annoying.
Thank you for reading.