Creating Tier 3 pieces requires a lot of gold, RNG and someone with an actual Tier 3 achievement! Here's what you need to do in order to craft a Tier 3 piece:
Loot a Lamented Crusader piece of gear from Zackett's Dented Gear tokens.
Repair the Lamented piece of gear by using one of the cursed Naxx items (Cursed Cloth,  Languished Leather,  Scourged Scales,  Undeath Metal). The recipes can only be obtained by someone who has the achievement  Drop Dead, Gorgeous from collecting a full Tier 3 set, but you can work order for these if you don't have the achievement. This will turn the piece into a Desecrated piece of gear.
Once you have a Desecrated piece of gear, you can purify it by using Phylacterweave and Righteous Orb:
 Purify Helmet: 280*Phylacterweave, 10*Righteous Orb
 Purify Shoulders: 28*Phylacterweave, 10*Righteous Orb
 Purify Chestpiece: 210*Phylacterweave, 10*Righteous Orb
 Purify Bracers: 70*Phylacterweave, 10*Righteous Orb
 Purify Gauntlets: 140*Phylacterweave, 10*Righteous Orb
 Purify Belt: 70*Phylacterweave, 10*Righteous Orb
 Purify Leggings: 210*Phylacterweave, 10*Righteous Orb
 Purify Boots: 140  Phylacterweave, 10*Righteous Orb
A complete set of Tier 3 armor will require 1400*Phylacterweave (or 2.8 million gold in vendor mats), 80*Righteous Orb.
Congratulations, you can now craft Tier 3 gear!