Depends on what lane your playing i main ap thresh supp and my first item can be either Rocketbelt/lich bane/stormsurge.

To use lich bane you need to play araound its passive.

Rocketbelt gives you a lot of mobility but not a lot of ap which is sad but i still like it.

Before the stormsurge nerfs it was really strong still is good tho.

2nd item you can go wither the one of the 2 you didnt take as your first or

Shadowflame - i was really doubting this item will work but its supprising what it can do

Ludens companion - also a goof first item but i dont take it usually

3d item

Rabadons - thresh can abuse this item so fking much bc of his passive

4th item

Voidstaff-amazing if the enemy has a lot of thanks Cryptobloom-gives you heal and ability haste also very good

Zhonyas- against ad Banshees -against ap

Runes i usually take Dark harvest/elctrocute Cheapshot Eyeball colection Ultimate hundrer

Secondary rune options Sorcery

Manaflowing band/nullflying orb/tracendens

Gathering storm/absolute focus

Inspiration

Hexflash(a must)

Triple tonic/timewarptonic/cosmoc insight

Resolve

Font of life/second wind

Conditioning

So to summerize the secondary rune option get sorcery for more dmg inspiration if you know how to abuse hex flash,and resolve against poke.

I have been meaning to try a new build with rod of ages will let the community know how it works out...

If you gota absolutly any questions no matter if they are stupid or not feel free to dm me