So the starting build #2 is Longsword and refill. pot. The reason you go with this is either when you have a very easy matchup or when you need to get your item a bit earlier.
And for the optional items, I recommend building the fist three items if you're against someone that is also tanky but with not as much dmg. The other three are very strong against squishy toplaners but the're not played often so you can struggle with this sometimes, mostly in teamfights.

Jax has got a pretty good laning phase because he has got a lot of dmg early and if you hit your combo (Q,W,E) you can get at least 50% of their hp (that's why Thunderlords') although champions like Darius have more early dmg than you even if they're AD, armor pen, attack speed is lower so beware. If you don't succeed in the laning phase, I recommend you go bot or mid and kill their squishies to get back.

There are two ways of playing teamfights. If you are tanky enough just jump in and stum everyone or if you are building more dmg try to focus single target and never jump in unless they're low.

Jax has got a very good outplay potential with his E. You have to pay attention to when you can recast it to stun your opponent. Example: You are 8/5/3 and their 13/4/2 Kha'Zix jumps on you. You instantly use Q,W,E and that means you are both low so you press E to stun and Q,W to finish him. Simple.