Okay, this is the best I have. If you want to bit it, the Chaos Marauder Fur cloak bit is good. Add some greenstuff as a head piece. To get that fur look, SPread your
GS as a thick blanket over cloak area, and let it get a little rubbery (like 10 minutes of set time), take a pick like sculpting tool (or even a toothpick) And poke and drag in tiny increments. You actualy want the tool and
GS to stick to each other bit, so it pulls channels and then points. Each one individually will look dicey at first, but usually the overall theme works. Also, if you decide it is too pointy, too raised, that actually isn't bad, just press it down gently in the direction you want your fur to flow without losing the creases.
I have a link to a picture of the cloak I mean, hope this works. These are a bits place I have ordered from, but i am not saying do so, just first pics I could find. I just am never comfortable recommending in case something goes wrong.
You also may be able to take a Wolf Guard type cloak and headpiece, and trim it to look like a giant rat.
http://www.ebay.com/itm/WARHAMMER-BIN-BITS-CHAOS-MARAUDERS-15x-CLOAKS-/331829350722?hash=item4d42921142
http://www.ebay.com/itm/W-AOS-Slaves-Darkness-Chaos-Marauders-Fur-Cloak-Bits-2-Bitz-/381764484273?hash=item58e2efbcb1
Wish I could help you more. I like your idea and hope you have some luck with this.