This Janna build is one I personally like to use. Even though I'm Silver as of release this build is good for a Janna player that like to roam and help others lanes once bot is fed. This build allows you to roam like crazy and slow people down with your W, Frost Queens, and Twin Shadows. Overall This build is fun to use and I encourage people to try it.

Pros: You move insanely fast and can slow others to hell and enter a fight from almost anywhere.
Cons: You out run most of your teammate.