This build has one main purpose. Go fast to get your carry fed. Overall you should go into the early game looking to make plays to get first blood and then bully your lane opponents out of their farm. Doing this successfully will help you scale into the mid and late game easily with tank and CDR items so that you are a menace in team fights.

I am not making this build to argue that it is better than whatever top build thresh players might be building right now. But it is definitely a fun build to run that can still work very well in a lot of match-ups.

Preseason has been a gem for supports and right now Thresh is an absolute menace. Courage of the Colossus is a huge buff for Thresh since 2 of his abilities are hard crowd control, allowing for huge shields to trade with and initiate with.

One thing you might be asking is, "Its preseason and we have Redemption? Why isn't that in here?". Well while redemption might be the most fun support item Riot has introduced in a long time, it might not be the most useful in ranked play. I have built it several times so far and always find it extremely underwhelming. Redemption has issues because it seems to either break up team fights (where enemies leave the circle while allies stay in circle, then the enemies just run away) or your teammates follow the enemies out of the circle and don't get the heal anyway. So far Redemption doesn't seem to be turning the tide of team fights as much as we thought it would.

Flash is an auto include on Thresh, flash hooks are hard, but can be game changing if done on a high priority target before a teamfight.

The big question is whether to take Ignite or Exhaust. Using Ignite will help you get some more damage off, and it could even possibly secure a kill. But much of the time when you ignite you will end up getting the kill instead of your carry. Exhaust not only aids your carry in killing the enemy laner, but it will also help to save them from dying and giving up their shutdown gold.

Be a good support, don't be that killstealing scum (even though you want to).

As said before, the goal of your items is fast paced tanky gameplay. If you can manage the pace of the game using these items then you can help secure your team a victory.

Core Build

Talisman of Ascension

Talisman of Ascension

This is your support item and will help you stay up on gold while your ADC is farming minions. It might not have as much gold generation as the relic shield line could have, but it takes your focus off of dealing with creeps so you can focus on protecting and provoking. It also greatly helps with sustain in lane so you can be there to pick up more gold from creep.
In addition to being your gold generation item this is also both your engage and disengage item for the early to mid game. Use it to get a jump on enemies in lane and force some flashes or favorable trades. You can also use this to get you and your ADC back to lane faster if the enemy bot lane is pushing.
Later on this can be very useful for roaming and getting good rotations.

Ruby Sightstone

Later after you have some other items, build this from your Sightstone. You need to build a ward item separately since you can't build Eye of the Equinox or Eye of the Oasis since you already will have Talisman of Ascension.

Knight's Vow

Season 7 is bringing this fantastic support item to the rift. It overall a great item to build to get tanky and to help protect your carry. One downside with the item is that thresh is a ranged champion, so the 12% damage heal/transfer is reduced to 6%.

Frozen Heart

This is an essential item to get built to get your CDR capped as fast as possible. It also supplies a large amount of armor for tankiness and mana so you don't run dry in a team fight. The mana you get also assists Turbo Chemtank in getting your health back while fighting. Getting 20% CDR in one items allows greater flexibility in the final build as you don't need to worry about getting an item with cooldown reduction.

Righteous Glory

Glory supplies the initiation and crowd control that you need to take charge of team fights. Since the rest of this build allows thresh to keep his mana up, you would be surprised how much health you can retrieve from using abilities when your CDR is maxed and you are throwing a hook and flay out every 4 seconds.

Boots of Mobility

These boots are amazing for catching enemies and roaming/rotating. If you want to use Boots of Swiftness as a substitution then you can, but I personally prefer Mobility Boots for the added chase potential. You also effectively give the speed to your teammate because you can lantern them in once you find an engagement. I usually try to get this item built after I have Talisman of Ascension finished but when I am working on Knight's Vow, but if you finish it before you get out of laning face then you should be fine.

MR Substitutions

When getting MR instead of the usual armor items, try to find cooldown reduction still. It will help you still take control of team fights and help you peel even harder for your carries.

Spirit Visage

If you are having issues with an AP enemy carrying the enemy then visage could be a useful substitution for Frozen Heart or Knight's Vow, Do remember that building visage and keeping Frozen Heart will possibly put you over your CDR cap if you keep the rest of the build the same.

Mikael's Crucible

Mikael's is going to assist your carry heavily in team fights from assassins and heavy crowd control. This can often replace Knight's Vow, but like I mentioned for Spirit Visage, be wary of your CDR cap and try to avoid going over it.

Locket of the Iron Solari

If you are having trouble in your team fights then locket can definitely help swing the fight in your favor. The nerf to Aegis of the Legion makes Locket of the Iron Solari not quite as powerful as it once was, but it can be useful nonetheless.

Situational Items

Zz'Rot Portal and Banner of Command

Both of these items will help you push lanes when you need it. I would suggest building Zz'Rot Portal when you are hitting your CDR cap and want to get tankier and build Banner of Command when you need another 10% to hit full CDR. Banner used to be one of my favorite items but again with Aegis of the Legion being nerfed it isn't as powerful as before in team fights.

Banshee's Veil

Banshees of course is built when the enemies AP is too much to handle. It is great right now against a lot of the assassins that have recently been reworked and can save you from being hit with crowd control at the beginning of a team fight.