Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Note: For my items, I usually get mana first, then upgrade to catalyst, then get swifties. upgrade catalyst to BV and then get chalice of harmony third and then sell that when I have 6 items to make room for another zhonya's ring.
This build is mostly for giggles. I find cooldown reduction to be very important when playing Janna because of the recent nerf to eots. with enough cooldown reduction your team wins.
Also note that its very important to get EotS to level 5 by the time you reach level 9!
With a level 5 eots on a level 9 tank or teemo your team wins no matter what they have, unless they have another janna with level 5 eots and a better teemo.