Shields - Requires proficiency to apply bonus to AC. Stacks with any armor.
Small Wooden Shield - +1 to AC. If enemy rolls a Critical Hit, shield is broken and useless. Weight 2 lbs. 2 gp.
Medium Wooden Shield - +2 to AC. If enemy rolls a Critical Hit, shield is broken and useless. Weight 5 lbs. 5 gp.
Large Wooden Shield - +3 to AC. If enemy rolls a Critical Hit, shield is broken and useless. Weight 8 lbs. 8 gp.
Small Metal Shield - +1 to AC. Weight 5 lbs. 5 gp.
Medium Metal Shield - +2 to AC. Weight 8 lbs. 10 gp.
Large Metal Shield - +3 to AC. Weight 10 lbs. 20 gp.
Tower Shield - +4 to AC. Weight 30 lbs. 50 gp.
Just throwing this out here right now. It's a work in progress. This, however, would make ACs way too high, as would Heavy Armor, so I might have to tweak AC bonuses for all armors listed.