When it comes to creating armor from scratch, I don't think much can be suggested here in terms of material the armor is made of. From the top of my head: leather (maybe different kinds), metal, polymers, some combinations of aforementioned... and that's mostly it.
But armor modification, that's a different story. Starting from stat changes, like adding combat plates to increase protection, through making the armor more versatile, as in adding a tactical vest or maybe adding "protection from energy attacks", ending with purely cosmetic stuff: camo, etc. Gaaaaaaary!