We build Decks and Porches also. We only used #1 Treated Lumber where possible. We have also used Trex Decking as well as Nexan Aluminum Decking boards. Decks also sometimes offer a new area below the deck for storage, or outdoor living area. Proper rail systems can have a strong impact with the right deck!
A Porch does not have walls, or screen, and is open. This separates the Porch from a Sunroom or Screen Room. Porches are normally protecting an entry way, or could be simply a roof over a deck or patio!