Hmm....its a tough one. there are various ways of making bare metal skins or textures. You can see our tutorial on this site which is aimed at IL2 but most of it can be transfered to MSFS:
http://www.simmerspaintshop.com/foru...ts-il2-fb.html
Basically, start out with a metal coloured outline. then overlay the panel lines and other details and then all you have to do is add shade and highlights. Carefull editing of the Alpha channel with add the reflective look to the plane.
The other way is to make a photoreal skin. In other words, use photographs of the actual plane (or any other suitable photos of metal) and build them into the skin. This is very time consuming and its difficult to make it work, but if you get it right, the results are stunning. See the pic below of the Beech 18 which has a photoreal skin and is probably the best metal effect I have ever seen. Hope that helps a bit??