There are many options for your roofing problems and not just aluminum shingles. Just make sure that whatever it is that you will use to replace your current roof must be very durable and has a long life span...
I think that it does need another support beem because if you are after the right balance for your deck then yu need to use another support beam for it...
Carpentry is a hard task but with determination and your willingness to learn, carpentry will then be an easy venture. Making decks is hard but if are determined to do it, everything then will fall into place...