This Is a pretty Easy thing to use. The calculations are off. Your Movement will be a little higher. You'll have well over 600 AP not 400 whatever, and I'm pretty sure you'll have a higher cooldown reduction. The Heal is amazing. Try it out if you want. This is meant to have fun so I wouldn't recommend this in Ranked matches.

I choose the quints because Cooldown is a must on this build. Seals can be swaped out fr AP seals if you think that the items and mastries alone will suffice for you Mana. The seals can be swaped out for AP seals if you wish, bu I wouldn't recommend it. Flat ability power Glyphs can be chosen aswell if you would prefer a stronger early game presence. If you happen to take Boots of Lucidity the Quints can be swaped for Flat AP quints as that will help you farm better Early game. If you feel this build is too squishy feel free to use more defensive minded runes instead.

The movement speed mastry isn't necassary. You can swap it out and put it somewhere else if you wish. The main reason I have it there is for the buff mastry so blue buff lasts longer. I wouldn't recommend changing the offense mastries as it's pretty much all yu'll need. This build isn't the best for being right in the middle of team fights and is more for cleaning up any weak opponents running away or taking out huge chunks of health from the enemy teams carries so putting mastries in the defensive tree isn't the best idea especially since you want to maximize your magic penetration and ability power.

Ignite is great on champs with heals such as GP or killing a trynd that's trying to get away with his ult. I wouldn't recommend swittching out Flash for Ghost since your ultimate gives you increased speed and will be able to activate it again if you happen to kill or assist in a kill of an enemy champion. Ignite can be swapped for exhaust. The other spells aren't really viable on this build so I wouldn't think about choosing those if I were you.

Pros:
Great farming
Amazing healing with Meditate.
Alpha Strike has insane damage and really good AP scaling not to mention that bonus damage it gives on creeps and jungle creatures.
Ultimate lets you get out of sticky situations and allows bck to back alpha strikes if you're getting kills or assists.
Meditate basically allows you to heal infront of enemies and tank turrets seing as it gives you 400 bonus magic resist and armor.
Hard to push out of lane since he can sustain for long periods of time.
Don't **** with this guy if he has blue buff.

Cons:
Is you're stunned or silenced you're almost as good as dead.
Early game is not the greatest.
Sometime a little too dependant on Alpha Strike and is heavily dependant on being fed/farmed and cooldown.
If caught alone you may likely die easily
Isn't a great 1 v 1 duelist especially against AD carries and tanks with stuns (Stupid Sion)
If solo laning you'll have to turret hug for a while.

Items are pretty much set. If you want, you can swap the Sorcerers shoes for Boots of Lucidity If you feel that getting off continous Alpha Strikes is more important. I would consider that if they have a tanky team. Hextech gunblade can be chosen aswell if you would rather have lifesteal to help sustain yourself and have spell vamp. Swap out Zhonyas Hourglass is you decide to go with the gunblade. Other items to help make you a bit tankier if you wish to stay in team fights longer would be Rylai's or Rod of Ages although I don't recommend these items seeing as I would rather prioritize Cooldown and Magic Penatration. Abyssal sceptar can be Bought as well if the enemy team consists of magic damage users and serves similiarly as Magic penetration seeing as it lowrs their magic resist.