I've played a lot of dps, assassin and carry heroes in this game but Lee Sin is far the best i've played.

I start of with boots of speed than go straight to mercury's treads that way Lee is good for ganking and running from a fight, then I get me some lifesteal for survival chances and recovery. the brutalizer is a very good item for Lee Sin get him a little armor penitration and damage to increase your lifesteal. than it's the phantom dancer to greatly increase attack speed for maximum damage and also movespeed to catch the enemies, than I buy B.F. sword and combine it with vampiric scepter and get the bloodthirster. next is avarice blade to combine with brutalizer and gettingyoumuu's ghostblade. now you got yourself great damage but Lee is still kinda vulnurable to damage so i buy warmogs armor for protection and last I buy Nashor's tooth to get attack speed and maximum your ulti damage with ability power.

I start with the sonic wave/ resonating strike becouse it's both good for ganking at early game and u can dash to enemies with it wich is kinda handy to hold enemies back from xp, then its tempest/ cripple to both farm minion kills and to slow down your enemies so it will be easier to catch them, the safeguard/ iron will skill is very handy in many situations such as saving a friend while he's running and to gain armor and life steal to recover after a fight, and last but not least it's dragon rage wich is a good spell to critically injure your enemies and also to kick them back while running away.

I want to point out that this is my first build I made so please comment and help me improve ;)