Your tunic is basically a tank top. Grab your grey fabric, cut out a tanktop pattern twice (front and back), sew the shoulders and sides and it should be snug (pic A).
LOIN CLOTH (Image 1)
For the loin cloth, cut a black strip of fabric for your waistline. Sew a grey rectangle onto it. If you really want to, you could sew a rectangle on the back side too, but the cape will cover that. I just used a safety pin to close the loin cloth in the back.
Cape (Image 2)
Grab a sheet of purple fabric and just wrap it around yourself. i just took the ends and wrapped them around my neck a few times, and then safety pinned it closed. (pic C)