The good thing about your idea of getting a roof for the deck is that during the winter or summer, it will be put to use indefinitely! I mean, the summer sun rays, or the winter snow will be kept off of your deck area. What is the square footage for this roofing job? I'm pretty sure some roofing companies charge per square foot, or they sometimes throw in deals with the more square footage you get - sort of like the concept of buying in bulk. You said you'd do this in stages, so it depends on how much square feet is in one of the stages. I assumed a standard roofing company would be around three-to-five hundred, but you'd have to get a quote for sure. Go with a company that's been in business for a long time too. Hope this helps, Armandochavez!