He's really easy to assemble, honestly. Put the arms in the right sockets(you can't get this part wrong), and put the torso on so that it fits the socket. Stick the head in the socket, and put the gob in the chest hole. Stick the flag on to the two nobs on the back, the horns beside the head, and the stikkbombs on the top.
Very simple to build. However, do to the sheer size and complexity of the kit, I recommend painting each part individually, THEN gluing it together. It sure as hell made my life a lot easier.