thorn mail or frozen heart?
Randuin's and tabis
Edit:Trick question, if the enemy is heavy ad, I'd go for the three items
Gotta go with Randuins. Mallet last if you have the extra cash. Trinity, Boots, BotRK, Randuins, Hextech is pretty nice to get first. If not Mallet, I'd recommend Warmogs since it's a little cheaper.
Edit: It's also pretty fun to build a little AP on Jax. Lich Bane/Deathcap in place of Trinity/BotRK. Or just Deathcap if you want the extra attack speed for the ult passive.
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