I'm not a great fan of equipment damage in games. I mean, yeah, stuff breaks in real life, but having to replace equipment every thirty minutes is neither realistic nor fun. So I would use a system where you need a skill roll to successfully block with a shield, but the shield takes either no or only minimal damage on a successful block. Probably less damage than the weapon, actually.
Also, don't underestimate just how effective a shield can be. I've play-fought both with and without shields (SCA and Dagorhir), and let me tell you, you never want to be the guy without a shield fighting somebody with a shield. The guy without the shield needs to actively protect his whole body. The guy with the shield mostly needs to actively his head and feet, because the shield already protects most of his body just by being there.