As a decent lee sin player I'd have to say that this build is way too expensive for what it offers. Tri force is only good on Lee if you're fed or you know how to use it's passive to the full effect. Imo Lee is about early dominance and he can't achive that with tri force. For Lee I ussualy buy parts of items that I upgrade later. Buying a triforce is just not worth it for early game dominateing champs like lee. P.S. Sorry for my bad english skillz. :)

This is a good build, but you should make it more aesthetically pleasing. It's basically a wall of text. Edit the style and you're good to go.

Many people say TF is a bad item on lee, but have you actually tried it? I love lee for his utility. TF adds utility. The mana is the only thing that is a waste to him-everything else he benefits from greatly. Although his auto attacks are very fast with his passive, it's scary fast with a TF, allowing you to work his skills faster whilst still taking advantage of flurry. I like TF on Lee, but it's not something I'd always build.

Builds like this are intended to snowball and win quickly. If I'm having a rough start I'd most likely skip out on TF and build tanky. Thanks for trying something different, sir!

Thornmail / Force of Nature is the optional sixth item I was aiming for, depending on the enemy teams main focus of firepower.

The effectiveness of this build is entirely up to the player and how they play Lee Sin in my opinion. I've generally had excellent experiences with this build, but I do appreciate the feedback given here.

The way I see it, a build like this might end up being seen as a "glass cannon" type of thing, in an effort to end the game early (20 min surrender) by shutting the enemy team down with relentless fury and teamwork. This tends to work depending if you play Lee Sin correctly.

In addition to this, I do agree that frozen heart is a strong item, but I feel that on Lee you can focus down an ad carry pretty quickly and disrupt them enough to be considered to be focused, which is where thornmail does come in handy. If I had to choose frozen heart or randuins, I'd pick randuins everyday and leave frozen heart for my tank. Also, I tend to stay with the MR defensive side, because you ALREADY get 140 armor from the rest of the build.

This build can be changed alot according to what you really need, I don't use FoN or TM every match by any means. Sometimes the necessary defensive item for me is Quicksilver Sash over more survivability. Thanks for your opinions though, I really appreciate it.

too expensive biuld and not so effective =\

Seems good build, +1 (Require comment to vote!!)
I think trinity works really well, but like said above, thornmail as ending item isn't really effective, but @Unicorn Frozen Heart on Lee Sin, is no go. just waste, but maybe guardian angel or randuins omen ?

Also the guide is overall quite brief, you should add some chapters like explanation of abilities maybe.

Like the guy above said, Trinity isn't so good.
You say you have 3.1k HP with this build. Atma's should only be giving 45 AD, in that case. Thornmail is nice, but I feel that it just encourages enemies to not focus you, and you don't have a taunt like Rammus. You should be soaking up more of the damage for your carry. Of course, if your team's too tanky, you're doing a majority of the damage, and the AD on the enemy team is constantly focusing you down, Thornmail is good (Guardian Angel works as well) I'd prefer getting a Frozen Heart in some situations to lower the effectiveness of champions like Xin and Yi who get affected quite a lot by it, even if it means wasting the mana component. Will have an effect even when the AD isn't focusing you, unlike Thornmail.

trinity is a subpar item on lee and ending as an item like thornmail is just a bad choice