Guinsoo's Rageblade is probably the best item on jax for farming and pushing lane. Since in ranked, early on, you normally wont be able to farm untouched, but if you do, it will not be smart to push your lane. Since if you push your lane you will be ganked. Early in games you should only last hit minions in your lane, not pushing it. Since Guinsoo's is mainly an item for pushing and farming you don't need guinsoo's early on. Rather getting items so you could deal more damage when "poking" your enemy in lane, and for getting kills.
If you're not playing ranked and you're "always" farming undisturbed, (facewrecking your enemies in lane) or not being ganked. You should then get Guinsoo's Rageblade as soon as possible, since with this item, you will farm like a BOSS, I can promise you that ^^

Hextech Gunblade suits Jax greatly, every aspect of this item is nice on jax. You get AD, AP, slow on activation, life steal and spell vamp. Allaround a great item for your sustain and damage output.
You should buy Hextech Gunblade in this sequence; Bilgewater Cutlass and then Hextech Revolver

Bilgewater Cutlass first for two reasons, hextech revolver has been nerfed from 20% spell vamp to 12%, and also for the slow on activation. Bilgewater Cutlass will give you 15% life steal. The life steal is nice combinating with Trinity Force' bonus damage, which is as physical damage.
With Trinity Force' slow chance and Bilgewater Cutlass' slow activation, it will be almost impossible to run away from you. The slow activation will help you get several hits on a champ which will increase the chance of slowing with Trinity Force too. |o|

Trinity Force is really nice on jax. It gives you 150% of your base damage as bonus damage on hit (after a cast).
That's the reason why I choose to max empower first, before leap strike....
Maybe you understand why now, but let me explain.

Cause of empower really low cooldown (3 sec in lvl 5), you will gain around 100 to 160 extra physical damage on your empower every 3 second. That's quite nice ^^

You should buy Trinity Force in this sequence; Phage, Zeal and then Sheen.

Phage first because of the needed health early game, with my runes and masteries the health from Phage is really effective. The slow chance is nice for getting kills. Why the slow chance is really good on jax is because when you leap strike on an enemy champ, and stun him/her, you will be able to get more than just one hit. That will increase the chance of slowing them for each hit.
The more tries you get, the chance of succeding will increase ;)

Zeal second because of the increased movement speed, and increased AtS which procs good with his AtS passive. The increased movement speed with zeal and the chance for slowing with Phage, decreases the change for your enemies to run away from you. Zeal gives you great mobility which makes it easier to dodge skillshots. It also helps you hit your stun easier; cause sometimes an auto attack will make you fall too far behind to be able to stun an enemy champ. Zeal will help you keep up and hit your stun even though. You don't need to run along with him and not auto attack him while chasing.

Sheen gives you a nice damage output, but Phage and Zeal is better for your survival and for chasing down enemies, which I think is better. Therefore I choose Sheen last.
Since I choose to rush Trinity Force, The damage from sheen, which increases pr/lvl, will not help you that much right away if you get it before Phage and/or Zeal. Sheen gives you 100% of your base damage, as bonus damage on hit (after a cast).

Ninja Tabi or Whether you choose Ninja Tabi or Mercury's Treads really depends on what damage type you fear the most, AD or AP. Solo top is all about winning and defending your lane. You will either be 1v1 or 1v2. If you are 1v1 buy your boots depending on if the champ you're laning against is AD or AP, AD= Ninja Tabi and AP= Mercury's Treads. If there is one jungler on your opposing team, you should consider your boots after the damage type that champ is too.
If the one thing you fear the most is CC, and not that the champ is AD, you could then also go for Mercury's Treads.

What kind of full boots is really game dependent, but if you went for Ninja Tabi, it could be smart to change to Mercury's Treads late game, cause CCs late game are deadly.