Here's what you'll need:
A really large hooded pullover sweater
It should be a lot bigger than you normally wear, preferably of just one solid color.
I got mine from the thrift store for pretty cheap.
Some felt, foam, or fleece circle things for suction cups
I used about 40 circles, about an inch and a half in diameter. I was lucky and found this foam mat with big circles in it I just cut out but you could just cut out a bunch of circles from fabric though. Or use real suction cups off a rubber mat, though that's more of a pain to cut out and sew on.
I used scarves and hats but you could also use batting, socks, newspaper, underwear, etc...
I sewed it by hand cause I didn't have a machine so I just had needle & thread, but it would go much faster with a sewing machine. Or if you're really in a pinch, fabric glue.