Not a bad start for an Ahri guide.
It makes me really sad though, that you didn't even mention the Greater Glyph of Scaling Ability Power as another option for glyphs. I understand that flat AP runes are nice for level 1-6 but after that, they are inferior to the Greater Glyph of Scaling Ability Powers. They already provide more AP at level 6, so please consider adding them.

Building Rabadon's Deathcap early really seems strange to me. It works on champs like Lux or LeBlanc because they have a very safe early game but Ahri doesn't.
Plus, the awesome thing about Ahri is that she deals good burst damage even without AP items due to the high base damage on her skills. This allows her to build the items with good sustain and utility as early game items, making her much more useful without lacking damage. (I think that's what makes Ahri so awesome.)

Well, these are my two cents.
I didn't vote yet because I'm waiting for your updates. :)

+1 good guide, though she's not actually on fire.

Thank you guys, I edited the voting. And also thanks for the feedback.

I use charm only as a CC in the begining, and with smartcast you can quickly cast orb of deception, and fox-fire. On the other hand, I use Fox-fire with ultimate, so sometimes i jump on him, with (R), and (W) and when he is running away, then I land the charm.
And thanks for commenting.

+1, I'd turn comment to vote on, nice layout, good info, mostly correct build minus the mention of Mejais

Why is fox fire worth leveling over charm, would you not want the charm duration to increase?

Turn comment to vote on. You should include Banshee's Veil as the last item so you have some survivability in there. Big green +1 from me :D

+1, looks good to me. You need some mana regen though. Your runes also fall off HARD late game, all flat AP is not good. I recommend removing Greater Seal of Ability Power and Greater Glyph of Ability Power and replacing them with Greater Seal of Scaling Mana Regeneration and Greater Glyph of Cooldown Reduction.

Otherwise it looks fine to me.