Hi, this is the build i think you should use, its the best for me, im SURE you will like it ;)

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I ve chosen these runes cause actually, the team who starts better usually wins right?, people get kill´s and they get too OP, so all this AP u got at lv1 make´s you kill te emo in 3 ice blasts per example, and don´t forget that, with all this cooldown reduction from masteries, you have this skill ready every 5 secs more or less.
Besides, at begin of the games, champs use to have 30 magic protection, if u have 9 runes plus 0.95... it makes that number run down to 21 . so they get too vulnerable, and u can easly get feeded believe me.

I´ve chosen these masteries cause u actually wanna ice blast everyone, everytime , and u can even hit 1k damage on hit, if you keep getting items like rabbadons cap or Majai´s soulstealer.
so ,you will start with a 24% of your cooldowns reduced, pritty nice isnt it? besides u penetrate 15% of your enemys�´s armor, witch its pretty cool.

I know i could start my built with a Rod of ages but you wont need it! believe me , doran´s ring will makes you even more strong at begin, besides u can use skills everytime and push as you want cause u have mana and hit very nice, and don´t forget nunu passive, every 7 hits you get a free skill,so don´t wurry you wont need mana runes nor items.
So...at begin u have +100life all mana you need and +15 ap! starting with 45 AP more or less and with lots of magic penetration...its a total pawnage!
Then why the boots...those boots are awesome, stun\slow etc protect, and as almost every champion atack with AP, you have mag resist on hem. (u can also choose mag penetration boots if you prefer).
Then when the game is starting to get lots of gang´s and so, u buy a giant belt , and this will give you a great help on team fights and so, cause you will be like 2k HP at this moment, so u tank and you hit very nice, no one will mess with you one on one like this.
then buy keep buying the items i suggest and if your opponents are all of the same type of damage (Ability power or atack damage) u can change it, if they go AP u buy a force of nature and if they go AD you buy a torn mail(this item gives 30%damage back to enemy!o.o) then, after you get your tank mode on, u just buy a rabaddon´s cap and you are OVERPOWER! :)

Thank you, any questions, ask me, be free to ask ;)