When I use a mage to fight Zed in mid, Should I go for Catalyst? Or shhould i get doiuble dorans into zhonyas(50 armor) or should i get them armor itemss

Zed is definitely a mid to late game champ, if you've got a strong early game AP then I'd suggest double Dorans to overpower him early game, he's either going to have to trade with you to deal damage, or he'll be spending a large amount of his energy to throw out a W>Q. None of that energy is restored unless his Q hits the same enemy twice, so he'll be low on energy, with a CD on his escape mechanism, and vulnerable for a short amount of time immediately after that combo. If you have the ability, that would be the time to deal some damage, before his Q comes back up.