Hi :)
This is my first guide - probably not the best , same for my english - and I ll try to tell you something about the champ Janna. She is often played as a support , I try to show you , that she can more than " just support ". Janna is a great mid champ with a lot of damage...

In this part , I ll show you the items I take Janna , if I play her as an AP-carry.
Some of them are probably changeable and maybe not the best , but yes , I ll go on ;)

1. Boots + 3 Health Potion // 2 Health Potion + 1 Mana Potion ~ Early substain at your lane + movement
2. Kage's Lucky Pick ( later -> Deathfire Grasp) ~ More gold ( -> burst damage )
3. Athene's Unholy Grail ~ Mana problems are gone , lower cd's , some ap
4. Rabadon's Deathcap ~ Damage. Just Damage. :)
5. Zhonya's Hourglass ~ Ap , Armor + the active, feel free to buy, but no must have!
6. Lich Bane ~ you 'll think " WHAT ?! LICH BANE?! " - Yes. The bonus AD of your Eye of the Storm makes it useful. Still good for tower-destroying.

Other items :
- Archangel's Staff ~ your cd's makes it not really useful - but still nice boost.
- Abyssal Mask ~ MR , AP + aura - great alternative for Zhonyas!
- Mejai's Soulstealer ~ Too risky. But if you are a fan of risks - feel free to buy it ;)
- Moonflair Spellblade ~ Anti-CC. But low AP. Better not!
- Rod of Ages ~ Life + Mana + AP - why not?!
- Rylai's Crystal Scepter ~ AP + life + slow. I don't think , that you need more slows with Janna , but i don't say that it would be useless!
- Void Staff ~ The enemy stack MR - BUY IT !

Ok... now the summoner spells.
Flash - Nice to hunt someone , great escaping.
Ghost - Nice ,too, but you have already much movement speed with Janna.
Ignite - Damage. Damage. Damage. - Just great!
Exhaust - Slow. I don't think, that you need it, but it makes you able to chase someone.
Teleport - You can easily gank other lanes or don't have to go the looooong way from base to lane ;)

Now better what I said to each of this summoner spells... they all are useful! I take normally Flash and Ignite ,but like i said - the others are useful ( + good) ,too!

Greater Quintessence of Ability Power ~ AP , mainly for the early game.
Others :
- Greater Quintessence of Magic Penetration ~ more Magicpenetration
- Greater Quintessence of Scaling Ability Power ~ AP , better for late game, but make you weaker in the early game.

Greater Mark of Magic Penetration ~ Magicpenetration to damage your enemy without too high "MR-problems"

Greater Seal of Magic Resist ~ MR for substain at mid, if you know your enemy ( as example Talon ) take Armor Seals!

Greater Glyph of Ability Power ~ AP = Damage. Just take it! ;)

• Nice slows + cc's
• Heal+Shield (Team-Supoort)
• High Movementspeed
• Movementspeed for the whole team
• Towershielding
• can survive a gank easily
• You get a lot of assists ( ... but no kills)

• High cd's
• Her Damage is based on 1 Spell
• Hard to get kills ( ... but a lot of assists )
• Items are really important
• Just 2 Damage spells

This is the "real" strength of Janna !
Her Q throw enemies in the air - in a team fight it's not difficult to target them.
With her Zephyr she damage one hard - the slow makes him unable to escape.
USE THE Eye of the Storm FOR AN ADC ( ATTACK DAMAGE CARRY ) !!!
- Why ? - 'cause the ADC 'll be the first target, so he get a shield which makes him able to survive long. The Bonus Attack Damage is great for him ,too!
Her Ulty ( Monsoon ) throw enemies away - and heal your allies! Use it to counter some spells... examples :
- Bullet Time
- Curse of the Sad Mummy

This is the End of my guide. I hope you like it, please give me tips and critics - I just can - and want- learn out of it! Please realize , that this shouldn't be "the best guide" , it's just a little one.
And don't forget if you play Janna :
YOU CAN CARRY YOUR TEAM! BLOW THE ENEMIES AWAY!