i wouldnt go for the def tree with lee sin. since they've nerfed his double cripple he will make a tad bit less gold, how ever i wouldnt go for the gold boost in that regard. in a 30 minute game it makes 160 gold, no thank you, i would rather gain longer buffs for that. i do agree tho that cool down req needs to be dropped, with flurry, the slight attack speed increase cannot compare to the help from cool down. perhaps consider getting the iron will up abit. remember it also gives spell vamp, which apon entering a fight when at half health a good placed cripple wont just line you up for slowing the creeps and the champ but you'll get fat dps from hitting a couple of creeps, this has been the slight little bit that has changed things for me, and helpd slip in that double kill.

I like the item build sequence.
The masteries I would change.
Def need to max out cd reduction and for jungling id go down defensive tree
Instead of utility.

I made a jungle guide as well. My feedback for you would be that without Wriggle's, you cannot kill dragon alone at level 6 or 7, and that sheen in an early game does you no good, but the rest is fairly similar to my own.