So if you haven't already one this game, you should finish your blood razor and go hunting for kills, you only have one space left in your build, and in there you are going to fit a Hextech gun blade.... yep that seems kinda hard seeing as it costs about 4K gold... But once you go this... you are basically god on this map. You will now be focused VERY hard in Team fights. But don't worry, once you have hextech you can just finish the game by letting your team push, or defend, which ever position you are in, and just sneak off to go solo baron and to the enemys surprise, your team ( who is ALL fighting them) suddenly has baron :D.
At this point it is just GG. Oh I almost forgot to mention tha once you have finished fighting baron, because of your life steal and spell vamp, you will basically have full Health and mana :D
Now go pwn sum nubs

At this point go for some more damage, the Blood thirster give you a good amount of damage, and the life steal to help you regain health and stay on the field longer.
After that just slowly build Blood razor, because once you get to late game the tanks will be very difficult to kill with all of their armor, as you may have seen, you have NO armor pen.....
The blood razor does 4% damage to their health no matter what armor they have so it is a great item for Jax since he can max his attack speed once you hit about 4 times( with this build at lvl 18)

It's simple, go for rage blade ASAP! It helps you get your attack speed up to the cap REALLY quickly one you have phantom dancer. With those two, and ninja tabi,you should be able to stand up fairly well against any opponent, in a 1v1 you are now going to win.... Easily

I've played Jax for a while, and I keep seeing other Jax go AP for some reason, there are a few that go AD as this build is, but none quite so effectively.
After testing this build in real games, I decided to see how much damage i could do just up against bots. After about 15 minutes against them it is basically a race to see how quickly you can finish you build.