I just like playing lee sin, and find that this build works really well for me. Just wanna share it with you all and get some feedback, maybe you have some ideas/improvements? I play him as a tanky dps, since that has been OP with most champs lately. Enjoy trying this build and let me know how it works for you!

Pros:
- does massive amounts of burst damage, but can also be played as continious dmg ( depending on if you want to spam your skills or not)
- uses energy, so no mana problems!
- can jump in and out of battle
- can take a beating

Cons:
- vulnerable to cc
- needs a good laning partner early game in order to succeed
- not great against creep waves early game

I take armorpen and defensive runes, this helps greatly in his survivability and dmg output. I feel armorpen is more effective than flat dmg or dmg/lvl, especially early game.

a bit more focused on offence then defence here, but for the same reasons as runes

I start with boots, because this makes harassing with Lee Sin easy.
I build attack speed for faster energy returns with his passive, attack damage because it scales with most of his skills, and tanky items because you need to be near people to hurt them, so you will need to be able to take a hit or two!

Edit:
If you are up against some heavy DPS players, Thornmail is always a good option. I'd trade it for hexdrinker.

I take safeguard/iron will first, because it also gives you early game lifesteal, and can save your butt! no use jumping in if you get killed the instant you arrive. the next two are sonic wave/res strike and tempest cripple, so i have all three at my disposal
i try to level safeguard/iron will first, followed by sonic wave/resonating strike. these will make you extremely mobile, durable, and give you damage in a fight. i lvl dragons rage whenever i can ofcourse.

Flash gives you yet another short distance teleport, adding to your mobility. also, flashing in front of someone and ulti kicking them to your team/turret ensures a world of pain for the enemy.

Ignite give you the advantage over more dps+lifesteal or hpregen champs, and it jsut gets you kills you couldnt get outherwise. and Lee Sin loves kills.

other options:
Ghost - dont get this because you should be mobile enough with this build
Cleanse - works well because you are vulnerable to cc, but i feel you shouldnt get yourself into that much trouble that flash and your other skills wont get you to safety.. then you are doing it wrong!

early game: first try to harass a lot. pick a good laning partner that can do the same. the enemy should be burning through their potions and summoner heals in no-time, and when they have, go for the kill. this usually works well for me (avg 5 kills/assists first 10 minutes), but this totally depends on teamwork with your laning partner and the strength,skill and chosen champs of the opposite team.

if you do seem to get low health from harassing, use safeguard on yourself and use the lifesteal from iron will on creeps to regen. this works even better once you have vampiric scepter.

mid game : if you are doing well, see if you can help teammates out by ganking. you are an excellent ganker with all those jump skills. Also, feel free to get some lizard buffs / dragons if you can. but watch those towers! I normally only do this if my lane is fine and the first enemy towers have been destroyed.

late game:
try to single out the squishy dmg dealers and casters in teamfights. also, try to land your ulti so that it hits all of the enemy champions for maximum damage. Try to flash behind the enemy and kick them into your team/turrets. If you get focused, jump to your teammates with safeguard and run!

So, let me know how you like the build and tips, and any suggestions/improvements/critics are welcome! Have fun playing Lee Sin, The blind monk!