so ive been playing Zed ever since closed beta, and stopped playing him for a while to climb, because his damage falls off a decent amount in mid-to-late game, especially with a long cooldown on his ult.. so i decided a few weeks ago to try out a pure CDR build[Black Cleaver, Serylda's Grudge, Lucid Boots, Navori Quickblades, Solari Chargeblade, and Trinity Force] that doesnt really focus on Armor Pen. so far, it's worked pretty well especially after getting 2 items, which lowers my ult's cd significantly, and the best part is that when i get full build (which has happened a couple times), the lowest i got was 23/21 seconds! it gets me decent damage and makes sure i can still fight for a good period.