This Darth Vader costume, is one of the easiest costumes that you can make yourself. All it takes is an all black outfit and three print-outs (links below).

Photo credit: Frosted Tips

Darth Vader mask: Print out of this mask

Black Long-sleeve top: Uniqlo

Black Faux Leather Pants: ASOS

Darth Vader Breast Plate: Print out of this image

Darth Vader Belt: Print out of this belt

Shoulder Piece: ASOS Jumper half worn over the shoulders

Black Cape: Hot Dollar

Black Boots: ASOS

Light Sabre: Rolled up red crete paper with red battery powered IKEAS lights wrapped around it