I kinda don't see the point of building Thresh tanky...

Diclaimer: I barely play him and if you go through my match history you might find only one game with him in which I tried out a random build. This is more about looking at the design and what it does, or what it is supposed to do.

Thresh is a utility support focussing in engage and disengage, either hook them, pull in and do the combo, or flay them away and save your teamates with the lantern while pulling up a spooky wall.

Now, what is the puropse of tanks? To last during teamfitghs and form a relevant frontline. Tanks engage and proceed to sit on the poor fool they have picked as their target, shrugging off all possible damage coming their way (or so it should be), while their team jumps on whoever they keep locked down during that time. HOWEVER, Thresh doesn't lock down people that way.

When you disengage, you don't need tankyness. A sucessful disengage means the fight is over. There is no need to be tanky in any way.

And when you engage as Thresh, you don't need to be exactly tanky either. You hook an enemy from the distance, and you just need to be tanky enough to do your thing and then take 3 steps back while your team wipes the floor with whoever you caught. No one will focuss you in a situation that is not a 1vs1, as a Thresh with his abilities on cooldown is pretty much sitting duck that poses no danger, as compared to the marksman.

Thresh engage pattern is not like that of an Alistar or a Leona who can only decide between not engaging and GOING FULL HAM INTO THE ENEMY TEAM. That's not how he works. And he gets no benefit from sitting on top of an enemy either. Thresh's role in a teamfight after a sucesfull engage is to walk back next to his adc and keep the lantern ready and hope E comes off cooldown fast in case peel is needed.

And usually, as Thresh you are the last one to die in a teamfight unless you are the one who gets caught: not because you are tanky, but because you are just the lowest priority target. And with that, tankyness seems to be a quite useless stat to invest in.

Personally, I had an interesting experience with the following build: (the game ended before I could complete it, we won I think...) However, the additional slow from gunblade was quite neat and the enemies always forgot about it, and I could actually help out my team kill stuff even if my abilities were on cooldown. The funniest part was the time when the enemy supp tried to duel me and I hit 8 rageblade stacks... the soul-aa-bonus counts as on hit effect... The result was quite hilarious ^^ As for other items, I would probably have build a Nashors and CDR boots for the 40%, as that appears to be the best stat on Thresh.