I have an idea that will streamline the game client greatly
In the summoner profile make a tab that holds all the items in the game along with a champion builder.
Why? Well there are other sites that have champion builders but we're at the mercy of people keeping up with patches and sometimes some champion builders really don't tell you enough.
An ingame champion builder/ item database would streamline the situation and enable people to have access to the most up-to-date items and champion stats reliably. Also the champion builder would enable to maybe test a build idea without having to go to some random website that may not be up-to-date or is having connection issues.
Note that people would not be able to publish champion guides on the client for several reasons, one: the sheer number of guides that would be present would make the client less open on the system requirements, and two: preexisting sites already have a large cache of good guides and therefore why do extra work when we can get these guides easily elsewhere?
So in short it would be a tab that would have general information on items that would be intuitive for both beginners and pros alike. I'm thinking it would be like the champion tab in your summoner profile