As Lee Sin, you'll always want a certain degree is tankiness. Directly answering your question, whether you build tanky or damage depends on three key factors:
- Your personal ability to make plays
- Team composition
- How well you're doing that game
Lee is a fun jungler and quite viable because he fits well into pretty much any team comp. However, many Lee players, especially in solo queue, fall into the trap of trying to carry with damage Lee, while tank Lee would have been much more useful in the situation you are in.
If you are confident in your ability to carry as Lee from the jungle, I would still suggest you build a maximum of two damage items (Hydra and Last Whisper). Get Golem (not sure how good it is now in pre-season 4 because it did get a huge nerf) and Ninja Tabi, Randuins, and it's all situational from there. Sightstone is also pretty much essential. Sunfire is not as cost effective and the passive doesn't really sync with Lee's kit, so I wouldn't recommend it.
Carrying from the Jungle as Lee Sin involves looking for opportunities, great mechanics (kicking an enemy carry back into your team, or Insec as it's known), and good game knowledge of where and when to be. It's certainly not at all easy, and if you try to build damage/carry Lee Sin but make the wrong plays, you'll just end up feeding kill after kill to the enemy team, especially in mid/late game when your damage begins to fall off.
It's generally much safer to play Lee Sin as a purely tanky/defensive peeler for your carries. Of course this is not as much fun, but it ensures that you're at least useful to your team. Stick with your carries and kick the enemy bruisers and assassins away from them. Slow their attack speed with your e. Give them a shield.
It's also important to factor in team composition. If your top and mid are both relatively tanky (let's say you have a Malphite and a Swain) then it's perfectly fine to build a bit more damage on Lee if you have the money for it. What isn't a good idea is building glass cannon Lee Sin when you have two squishies top and mid, and a squishy support.
Obviously, your build path also relies on how much money you have in the game. If you're doing well, don't hesitate to pick up a damage item or two. However, if you're behind, it's never a good idea to build damage on Lee Sin. Defensive items are generally cheaper and help you peel for your carries better.
To sum it up, your build for Lee Sin should depend on your own personal skill (which determines which role you are going to fulfill, a play maker or a peeler), your team comp, and how well you're doing in the game. You can certainly carry as Lee from the jungle, but if you're not that confident in your ability to it's a lot safer to just build tank and peel for your carries.
Best Answer
Yes he is targetable during the whole flight this means you could even stun him with an udyr autoattack if you are fast enough. A Blitzcrank/Thresh hook is obviously pretty hard to land on a flying Lee Sin but With a thresh E you can prevent him from dealing any damage which is actually pretty easy to time with smartcast on. Here you can see that it is possible with thresh E.
You can interrupt most dashes with hard CC. The only exception to this are dashes which renders the Caster immune to CC (Vi R, Malphite R) or that make him untargetable (Maokai W, Master Yi Q)