Lee Sin is a great melee jungler, and is fun to play.
He can be very dangerous early game if he knows how to aim his Q, and he could also be dangerous late game if he is fed early on.

Explanation of why you get these items
Firstly I would like to thank you guys for reading and using this guide, and you would get:
A hunter's machete first because it will give you a quick start on damage to minions so you can get easy CS and can kill off red fast.
5 health potions are needed to give you sustainability so you can keep farming for EXP and gold.
A brutalizer is perfect because it will give you a great start on attack damage and good clearing speed.
You top it off by getting a black cleaver because it gives you health, damage, and armor penetration.
With this, at early game, your ganks will be unstoppable.
I would go for a madred's razors because it gives you armor and it stacks up with your hunter's machete.
After that, you can go for a wriggles lantern because you can "ward jump" and it gives you a good amount of armor, helpful amount of damage, and so you can easily get CS.
After this, you will want to get a head start on lifesteal so you can sustain longer and get a good amount of work done.
Bloodthirster's are perfect for this job because they offer a lot of attack damage and also a lot of lifesteal.
You will want 1 of any boots. You don't get them early because they have no use to you because if you need speed, just jump around with your Q and your W!
If they have a lot of AD players, get a ninja tabi so you can fend them off.
Therefore if they have a lot of AP players, get a mercury's threads.
Berserker's Greaves will give you a lot of attack speed so it won't be bad, but since you won't be building too much tank, you might want to get some MR or armor.
A trinity force offers TONS OF DAMAGE (haha Phreak) and will give you all you need.
AP for the shield, AD for you clearing speed and takedowns, and armor so you can tank a bit.
To end this build, you will want a infinity edge so you can take down the enemies how much times you want.
You will want this at the end because you won't really need it early.

For your first skill, you will want your E (tempest / cripple) because it does AOE damage and offers you some attack speed for your hunter's machete.
After, you will want your Q (sonic wave / resonating strike) so you can gank and do good damage to minions and so you can just fly everywhere.
After you will want your W (I don't know the name for this lol) so you can shield yourself, get lifesteal and armor so you can sustain in lane or jungle and also run away using your wards or your wriggles lantern.

In my opinion, Lee Sin is like a ninja and is extremely fun to play.
When I first got him, I used him more then 10 times in a row.

This is what I do to gank in ranked games.
1. Q and jump towards enemy.
2. E to slow down enemy.
3. Keep chasing and fighting. If they run, your plan is going alright.
4. IF they fight back, use W and try to fight.
5. If you are losing the battle, ult them to run or W to run away.

This is what I like to do with my ult:
1. Q towards them.
2. Slow them.
3. Walk to the front of them.
4. Laugh at their face.
5. Kick their face so they fly to your team or your turret.

If you want to counter Lee Sin, you need a lot of CC (crowd control) so you can walk in front of him so he can't kick you back to the turret.
If you manage to CC him, run as fast as you can to your turret unless you think you can take him.
Highest chances are you can't unless your Vayne or Xin Zhao or any character with lifesteal and a lot of damage.
If he manages to kick you to the turret, your pretty much dead, so try to just give the support a kill if he/she is nearby.
If you manage that, Lee Sin won't get too fed.
If your playing a character with ninja-like moves that could jump from like wall-to-wall, then try to go through the walls near a turret.
If you have NO CHANCE and there is NO SUPPORT nearby, just punch the turret, because there is no chance of escape and you might as well push.