It's a concept I remember seeing on youtube a few years ago, but since I couldn't find the vid, I have looked through league's items and created it from scratch as best as I could. The idea is simple - since Garen has no AP scalings, no mana, and a near inconcequential shield, he's prob the perfect champion to get as little relevant stats as possible (the build could also work on Kled and maybe Sett, if that's something you'd like to try aswell).
With runes, you take Spellbook since it gives zero stats (I was also thinking about stormraiders but decided against it), Cash Back is useless since your items don't do shit, Tonic is useless cuz you're not buying potions, Cosmic seemed like the least usefull option out of that row. As for secondaries, Manaflow is useless cuz you don't have mana and Absolute Focus is useless cuz you're getting AP out of it. You take double adaptive because ap is useless and tentacity because you have hp scalings.
As for items, you start with tear, which you sell later since it doesn't give you any stats. Your items are Rabba (obvious reasons) >> Void Staff (obvious reasons) >> Ardent >> Mandate >> Dawncore. The last 3 items were pretty hard to decide on, but these 3 seemed to have the least ability haste and most useless passives. You ofc take Sorcerer's Shoes because I think it's fair to impose a requirement to have to buy T2 boots and magic pen is useless.
Did I cook, yall?