Instructions
Buy a Costume
Purchase an Organization XIII robe. Because all Organization XIII characters wear the same outfit, you need not locate a costume tailored specifically for the Zexion costume.
Purchase black boots and black gloves. You need not purchase boots or gloves specifically made for "Kingdom Hearts" costumes as there is nothing unique about the black gloves or black boots Zexion wears. Because the boots are hidden by the long robe, the height of the boots is unimportant, so long as they extend past your ankles.
Purchase a Zexion cosplay wig. Zexion's spiky hairstyle is difficult to replicate; a Zexion cosplay wig gives you instant spiky, silver hair that covers half of your face.
Homemade Method
Make an ankle-length black robe. Model the robe after the Organization XIII design. The robe is held together by a long zipper down the middle of the front.
Purchase black gloves and boots. You can make the gloves if you like; boots are more difficult to make and may be the one item you must purchase ready-made.
Dye and style your hair. Dye your hair silver temporarily and add some black highlights at the tips of your hair. Style your hair with hair gel. Recreate Zexion's spiky style with long bangs that cover half of your eyes.