Picking the Tome first really cuts Twisted Fate short compared to buying a Doran's Ring.
The HP and mana-regen are important for him to survive and cast.

Mejai's always a gamble, so making it part of the core is quite questionable.

Thanks for the input. i see where you're going with the mejai's and nashor's. you could definately push the mejai's back and move the nashor's up a bit, but i tend to exploit enemy squishy's like ezreal, yi, ryze, etc. very early in the game. and i do agree with you about the masteries, it would probably be better to go with a standard 9/0/21 caster build.

if you go ap, you should get wild cards first, imho. maybe mana regen glyphs. personally i dont like to get an item that stacks with kills and un-stacks with deaths, untill about mid-gameish when i know i either wont be getting the kills/assists or if they kill me every 3-4 kills. sheen and lich bane are good choices though. i also would like to see nashors tooth a little sooner maybe, or at least the fiendish codex, for the mana regen and cooldown reduction. maybe put more masteries in utility if your going ap. take at least 2 points out of alacrity, put them to use for mana regen, your wild cards will do lots of damage so use them often enough to exploit the damage, which requires mana regen since wild cards is a mana eating *****. take out offensive mastery, its not doing much good, wild cards will severely damage a wave of creeps and red card can help clear them out as well, 2 more damage to them is minimal considering your damage output as ap tf.
you also wrote a really good description. i'm glad to see i'm not the only one who exploits the blue card for the mana, it is exceptionally useful as ap though. if you just win a big team fight and you used alot of red and gold cards you can blue card your way to full mana on your following team push. good build, i wanna try ap tf more often i might use your build as a base.