This is what I knocked up over the past couple of days for DS, to be used at the usual Freshers' week fancy dress party and/or Halloween party. It's based on view C of McCall's M5550, lengthened to the ankle and with inverted pleats added to side and (introduced) back seam from high waist downwards to give a bit more fullness at the hem.
The 'brooch' fastening is a couple of bits of grey grosgrain with some silver cord stitched in a spiral. It actuall fastens with buttonholes on the right front and buttons and a popper on the back of the left front.
He has a Palpatine mask (which is hideous!) and he acquired the light sabre recently for the purpose.