[Templar Mikeel]

All you need is a chassis to base it off of. It can take the form of literally any 40K vehicle out there. From there, all you have to do is add some Orky gubbinz, some dakka, and plenty of pointy things! If you're worried about the space factor, add a bunch of handles and tell your opponent that the Orks hold onto the handles!(even if they are on the side of the vehicle)
Battle Wagon Bits can provide you with most, if not all of the supplies you'd need for this. The only thing they don't have is plasticard which might come in handy.