Since the Ahri get nerf u must buy her a lot of ability power in the start so i recomand first building rabadon...After that you can go for crystal scepter cuz you will need a lot of health in a late game...Athenes unholy grail will help you with your cooldown reduction and you will cast your spells more quickly,making you an truly assasin...Build zonya for getting out of trouble and extra ap...Lich bane will help with abouth 600 damage from auto atack whenewer u throw an spell....Try this build and enjoy...Make some kills...
GL & HF!!! :)

Abouth the runes dont take glyphs per level take gluphs for 1.19 ap...