Welcome :) this is just a very quick guide, for now, since i'm planning to evolve this and modify it during the next days. for now, i found playing Lee Sin as a semi-tanky DPSer works very good, and i want to share with you my (poor, for now) experience with him.

i focus on defensive runes for seals and glyphs, while taking armorpen for marks and quints. HP quints also work very good for the early game, but i think it's a matter of playstyle.

i've seen many Lee Sin using Sonic Wave as first ability. while this is of course good for ranged lasthitting and harassing thanks to the gap-closer, the damage boost isn't that great this way, and your shield is too weak to be of any use. leveling the shield, however, gives you a very high amount of lifesteal, spell vamp, and bonus armor, wich are quite interesting during the early game. you can regenerate a very high amount of health on a minion wave, and your energy bar + doran shield assures you won't be easily forced out of lane. also, shielding your teammate can save him multiple times. and a 30-60% AoE slow is something IMBA. so get them, the %-life component on Resonating Strike will ensure that your first skill still deals damage.

for the items, i go for a Sheen first. your abilities have long cooldowns, yes, but they're easily chainable so that you end up with an ability every two seconds very easily. Ghostblade gives you armorpen and a good amount of speed and damage.
after building those two, you may choose. you can go for banshee/omen first (i'd say banshee, since you already reach a good armor amount with iron will), building up some defence, or rush triforce if things are going really good. i suggest to take Phage first. it gives some hp, damage, and a on-hit slow. Zeal is good, but you don't need attackspeed that much. you already have ghostblade and flurry for that.
after those two (defensive + trinity or trinity + defensive) work on your Bloodthirster. it boosts your lifesteal (30% from iron will + 15-25% from 'thirster) and damage. i know it's not the best offensive item generally speaking, but it's the only way to get damage and lifesteal on a single item, and you need to regenerate your health while fighting.
as last item, close with a second defensive. armor if you got magic resist, magic resist if you got armor.

for now, it's all. wait for an update :)