Right, before we go any further, this is really just me vomiting up something after getting all misty eyed for the old 2nd Edition Piecemeal Armour rules from Combat and Tactics. Its not been playtested, and has not been checked for balance. However, given the additional considerations I've put in, I can't see it being horribly unbalanced.
Ok, so, this is also one of those "Why would I use this?" type things, and again, I'm not saying you should. I like the idea of building a piecemeal suit of armour from scraps you find, and can see how I could use these rules to create "Set Items" like those found in Diablo or similar. I also like the idea of enchanted versions of piecemeal armour, where you might be tempted by dropping some AC to get some properties, without having to completely sacrifice wearing at least some parts of your current armour.
These rules awould also work well for any game where survival and conservation of resources is a theme, allowing you to modify your armour as you find scraps here and there.
Anyway, enough of me babbling on. Here's the rules.