Okay first of i will start telling this i my first guide. Also this isn't just a theoretical build I use it every time i play Twisted Fate

Icon 1: How the builds looks out in short terms.
Icon 2: A more detailed look on when i buy items.

PS: English isn't my native language so if there is any kind of gramma/spelling mistakes please let me know :) (if i use "i" instead of "I" i dont care :p)

Check out JunSupport guide too: http://www.mobafire.com/league-of-legends/build/twisted-fate-ap-for-premades-utility-carrying-23215 which has alot of details and i really enjoyed the read because there is some tactics etc, that i wont include because you can read them in that one :)

Pros:

Long range.
Can burst as hell.
Fun to play.
Excellent kiter if handled correctly.

Cons:

Squishy.
Hard to master due to Wild Cards.

I'm using standard caster runes you can however choose to replace Greater Glpyh of Force with Greater Glyph of Potency but choose whatever you prefer.

Masteries is pretty much again a standard Caster 9/0/21, where you can if you choose to change around if your gonna use other Summoner Spells.

Ok here i take Flash and Ghost because of the fact that Twisted Fate is a squishy champion, and the lack of any real escape mechanism.
However there is some other Summoner Spells you can use if you want to only use Ghost or Flash:
Teleport
Used together with Destiny/Gate you can have a fair amount of map control, for example by Teleport to a chosen lane, push it and afterwards escape or push another place with Destiny/Gate if necessary.
Ignite
If you enjoy extra firepower or just want a healing reduction you could use this spell however i don't recommend it because i never really have found use in the extra damage it provides.
Clairvoyance
An excellent Summoner Spell to Map Awareness, and reveal enemies with having to use Destiny/Gate, i however never use it for 2 reasons. 1: I sick placing it. 2: Because if going after full AP carrying, i prefer letting this go to the support and use my Destiny/Gate to support if i find it necessary.
Exhaust
This can be a good spell for you to use in the start because of the fact that you maybe not is quite as good as you should 2 stay on max range or if you aren't so quick to choose your Red Card / Gold Card

Choosing between Flash and Ghost in case you only use 1 of them:
I would say that you should take whichever of them you find most useful, me myself however would use Flash because i like using it when it comes to quick finish an enemy of, or simple just getting out of a nifty situation.

Okay most of the items is pretty straight forward, but there is some of the items i would like to explain further.

Lich Bane

This is the most important item in your build and the reason that Ability Power Twisted Fate is viable. When you use your Pick a Card the Lich bane gets activated, so when you have chosen your card, and throw it you can and will hit hard as hell and when you reached late game with 20 stack's on your Mejai's Soulstealer you will have around 900 AP and that combo will take over half of those squishies health, where if you used chose your Gold Card / Red Card safely can finish them off with Wild Cards
CAUTION: You only take this item as number 2 if you took Mejai's Soulstealer else wait to get it after Rabadon's Deathcap

Mejai's Soulstealer

Okay this item i wouldn't suggest for starters because its only effective if you can safely maintain your stacks, its not required for this build to work and in some games you will not have the chance to get the kills early enough for it to be effective. Start building Rabadon's Deathcap if this is the case.
If you don't take Mejai's Soulstealer i would replace it with a Banshee's Veil later on preferably after your Rabadon's Deathcap and Lich Bane are finished.

Zhonya's Hourglass

In the games where you have chosen Mejai's Soulstealer and have just finished your Lich Bane its time 2 consider if this item would be more helpful in your current situation, than Rabadon's Deathcap due to its passive which can save your *** from ultimates and to be alive those extra 2 seconds that maybe can save you from losing stacks.
CAUTION: Against Karthus i higly recommend this items before Rabadon's Deathcap due to the fact that his ultimate will and can kill you, because of the fact he can use it after his death. There is very few situations where you not should start with this item against Karthus.

Boots

Okay the reason why i chose Sorcerer's Boots over Boots of Lucidity is because I cant find the need of extra CDR, because you from your talents got 9% CDR and from a blue buff an extra 20% which adds up to 29% and if you manage to get your Mejai's Soulstealer on 20 stacks you will get an extra 15% which will be a total of 44% (cap is 40%). And even if you dont get those last 11% CDR it's not gonna be a big deal, i rather have the Magic Pen over the ekstra CDR.
You can however in some situations if you fell CC'ed alot take Mercury Threads. I know you lose a good chunk of Magic Pen, but your no good if you dead.

When to Sell Doran's Ring

This is by far my favorite item ingame for Twisted Fate even though you only use it in start of the game. It's give you everything you could wish for early game: HP, Mp5 and of cause a lil' bit of AP. The hard part is when to sell it. Personally i often have it to the point where i need 200g to finish my Zhonya's Hourglass but sometimes when i don't find any need in selling it because I'm having a good game i often sell when i only need my Void staff or because i need space for Wands. But of cause its up to you when you choose to sell this favored item of mine.

In order to be a successful AP Twisted Fate you need to be very aware of what is going on around you in teamfights. You are squishy and the enemy know it thats why you will need to master Wild Cards so that you can run in and of of range from the enemy while throwing your Wild Cards and do tremendous damage to their health.
You should when your Pick a Card get close enough 2 use it on 1 of the enemies preferably a carry or a healer/support, and afterwards get away from their melee's and carry which can trap you and kill you in a matter of seconds.
Therefore play careful and know what is going on for without the necessary AWARENESS you wont be any good and might as well take a caster champion with more range abilities.

Okay this ability is basicly a 3 in 1:
Pick A Card
Cast once to shuffle the deck and again to choose your card, enhancing your next attack.
Blue Card deals 30 / 45 / 60 / 75 / 90 (+40% of ability power) bonus damage and restores 50% of the bonus damage in mana to Twisted Fate.
This is your primary source of mana return, and you should use it to last hit minions while you harass your enemies with Wild Cards
Red Card deals 30 / 45 / 60 / 75 / 90 (+40% of ability power) bonus damage plus his attack damage to units around the target and slows their movement speed by 30 / 35 / 40 / 45 / 50%.
This is the card you chose when your hunting down more than 1 fleeing enemy, because of the AoE slow.
Gold Card deals half the bonus damage of Red and Blue Cards (+40% of ability power) and stuns for 1 / 1.25 / 1.5 / 1.75 / 2 seconds.
This card is the most important card you have in a team fight even though it only do half the damage of the Red Card and Blue Card because of the stun. The Gold Card is a lifesaver and can turn the tides in a teamfight if you hit the correct target at the correct time, for example a Katarina channeling her Ultimate, or a Soraka that almost is ready to cast her heal to save their carry from the first round of damage.

Choosing between Red Card and Gold Card in following situations:

1v1:

Okay if your used to use Wild Cards i will recommend using your Red Card to maximize your damage output, else you a Gold Card if your not sure i cant hit him when he is not stunned. If your against an opponent that you know you cant beat, use a Gold Card to get them stunned and begin to run.

1v2:

Okay if your not late game and you cant finish 1 of them off quickly find your Red Card get them slowed and run as hell. Use your Destiny/Gate when you get far enough away from them if necessary

2v1:

Basicly the same as if your 1v1 use your Red Card to maximize damage and hit them with Wild Cards afterwards, and again if you cant hit a moving target use Gold Card.

2v2:

Okay your choice here can have the impact on the fight you and your partner is about to enter. If they have a squishy and your partner is either a melee or a skill-shot champion (maybe bot) use your Gold Card when you get close so your partner if melee can close the gap between him or her, or so that your skill-shot partner have an easier time hitting the enemy. Hopefully the 1 you took as target is now dead, else hunt him down if you can to finish the job, Now it has either turned into a 2v1 fight or the other enemy have fled.

If you can grab a Side lane, for 2 reasons.
1: You don't get any real benefit from being in Mid lane instead of another champion on your team who have 1 of those ultimates that really can benefit in an early teamfight + they're maybe just better for them if they get in a Mid lane for example with champions like Karthus, Annie, Ezreal and Lux.
2: You have the ability to harass 2 champions champions with 1 ability, and with a good Lane Partner you can be able to grab some double kills in most games. I also find it alot safer because of the fact that you don't have any items like Rylai's Crystal Scepter or anything to give you more survivability and no real escape mechanism.

Okay the next section is from personal experience and you maybe have a completely different look at it.

Partners

Nocturne
My favorite laning partner by far, he has his Duskbringer ability and his Fear, so you both got some sort of CC and Range harassment. Besides that its fun to go "hunting" when you both hit lvl 6.
Renektron
Because of his charge and stun you 2 will be a great combo, because of your CC and burst damage you will be able to pick an enemy out and kill him.
Soraka
Now you probably think im crazy but Soraka is a great laning partner for TF. You will be able 2 stay in your lane for a ******* eternity, because of her healing and you both have a way of getting mana back. however while this probably not gonna be the combo that get the most kills early game, i promise that your enemy will get to hate you with your harass and her healing.

Enemies

Without going to much into it stealth heroes like Twitch, Evelynn, Shaco and Akali because they all will get a chance to get way closer to you that you will prefer and therefore you will need to play carefully and for god sake buy some wards either you or your laning partner, because it can either save you or grant you a kill.


More enemies and laning partners will come soon ^^

One of the main reasons i chose to play AP Twisted Fate over AD and Hybrid is because i don't like the idea of the 2 others builds .. here comes why:

AD

I know many people swear to AD Twisted Fate because of the insane damage output you can have on a single opponent and your ability to rape an opponent before they ever gets out of the stun from Gold Card. The main problems i see in these kinds of builds it the SHORT range that Twisted Fate has. Sure you can hurl out tons of damage 1v1 but in teamfights you are an easy target because of the squishiness and the danger you can be if not countered. I choose AP Twisted Fate over AD also because of the fact that your Wild Cards will do a tremendous damage in teamfights where even though your Red Card hurts, you still gets more AoE damage from an AP Red Card, Wild Cards Combination.

Hybrid

Well I cant really come with some direct situations here because of the fact i never really have tried this more than a couple of times. My own experience shows me its quiet effective but I think its a slow build to get rolling, and again as Hybrid you will need to stand way close than i prefer with Twisted Fate, and the idea kinda goes off a Hybrid build if you just gonna stand on long range and throw Wild Cards, you could use an AP build more then.

Okay while I at the moment think I'm done with this guide I'm sure i will find on something to add later on :)
I Would love any kind of feedback positive or negative (constructive criticism is always welcome)
Hope you enjoyed to read the guide just as much as i enjoyed writing it :) GL with Ability power Twisted Fate and remember

"The House Always Wins"

Well because this was my first guide i couldn't get it to show for example the item icons with a tooltip when you moused over, or the Summoner Spells so if any of you can please tell me what i have done wrong i will probably update the guide a little after little when i get the time to do it :)