If you have played Dungeons and Dragons, you probably were the biggest idiot and died all the time.
No two armors are alike, nor are any two players. Each have their own skills, each have their own bonuses, and each can do things others can't.
You have a few sets of various armors... Such as chain, leather, plate, etc... Each of these have their own various categories, half plate, mithril chain, etc... Then they calculate the players dexterity and natural defense, add a set digit for the class, maybe one for the race, and then any extra spell bonuses, potions, skills, etc added on to make the armor better, or worse.
There's bonuses and negatives, it's all possible.
I say if you're making an RPG, at least base it off of the original, which happens to be Dungeons and Dragons. From there you span, no where else. If you want creativity, use the premades in there and alter those... No other method is going to get you the best, and will probably only get you laughed at.