Just a quick build question

Hi I'm the average silver/gold player and i have a quick question about mid lane. I main mid and mainly enjoy playing as late game mages (anivia, velkoz, azir) I'm usually comfortable with my build path but have run into a certain problem a few times. When I'm playing as a mana heavy mage, lets say anivia, and I'm facing a zed in lane the smart decision is to build a morrello or tear instead of athenes. But what if they have an ap heavy top laner (rumble, vlad). That screws me over hard. So basically all I'm asking is how to build mages vs ad but there's still an ap threat on the enemy team. Thanks for the help.