Hi there,
This is no Metal tutorial but I have used this to make around 40 squad skins that ALL have a metal look to them. I had to think of a way of making a quick metal look to all the skins I had to make (as making individual metal skins would have been a nightmare) so I came up with this Nightshifter's Bare Metal Skin Template
This file is in .png format so make sure your paint program can use this format or it will not show all the layers. I know this isn't exactly what people are looking for but take a look at my forums page (link is above my Sig. picture) and look in the "Official Squad skins" section if you are curious about how many skins I used this to make.
Hope it helps someone.