Trust me ;^)
Not Updated For Current Season
Threats to Ahri with this build
|Lux||Lux can bind you but if she does just charm her as most luxes love to proc their passives|
|Karthus||No mobility and zhonyas works well against him|
For me runes are always about damage early. The damage from the flat ap runes gives a slight advantage in damage when you are in lane and can sometimes win the lane for you.
Creeping / Jungling
Jungle Ahri is is an interesting playstyle. You have to kite with the movement speed your Q gives you. Very mana hungry and needs most of the blues. Very weak to counter jungle though. Ganks revolve around you landing your charm as your only cc.