Are there rules about mailboxes?

I am going to be getting a new mailbox, and I am curious as to whether or not the post office has any rules about the size, shape or material that a mailbox can be made out of. I want to get something a bit different from the normal mailbox, though not too different. I just want to get a nicer mailbox, but I want something that will be relatively sturdy and a bit larger if that is at all possible. I get a lot of magazines that tend to get wrecked when there is a lot of mail to be stuffed in the box.