Take these words for example:
木{もく}造{ぞう}: made of wood; wooden
and
金{きん}製{せい}: made of gold
I have been under the impression that -製 is used for where an item has been manufactured (i.e. Made in Japan; Made in America), or the manufacturing of a certain product (i.e. iron manufacturing, etc.). I also thought that -造 was for what material something is made out of. Flipping through my dictionary it seems -製 is more common than -造 for referring to the material used (e.g. 鋼製: made of steel).
Is there a rule about which materials use -造 and which use -製? Is it just something one has to learn?