The way you're supposed to fight him is to get him in to a fairly open area, dodge his attacks, and then hit him (don't touch his chainsaws) when he pauses to pose.
If you want a really, really easy way to beat him, go to the gun store and get a sniper rifle, start the fight, lure him to those two signs beside the canyon, and climb the bottom sign. He can't hurt you there, zombies can't hurt you there, and here is the kicker: he will always stop to pause in the same two or three spaces. Always. This makes sniping him not only easy, but incredibly hilarious.