I have read nothing of shields for DayZ yet and i really think it'd only benefit it. Society has devolved to hunters and gatherers and half the combat is melee so it makes sense that human ingenuity would allow for adapting car doors/signposts signs/wooden planks/ boards into defensive items. Melee weapons have the 'spacebar mode' where the weapon cannot be used and is raised in front of them, this mode would be perfect to toggle on/off 'shield mode' instead. As far as quality goes wooden would be lowest up to scrap metal shield and military grade riot shields as highest. One thing that i found really unimmersive about a zombie apocalypse is the lack of protection the survivors seem to take. Let me know what you think.