It's really not a good idea to approach a roof replacement off the cuff with no checklist, no planning, and no knowledge. Being disorganized is the fast path to losing money and maybe even getting sued if someone gets hurt on the job. Make every effort to contact the right official offices in your state for any guidance you may need.
It is possible to have eroded areas or any kind of early signs of damage visible when you're on the roof itself. Catching problems and the early signs of moisture damage or water seeping through or whatever will pay for itself because it can be like a cancer on your roof. Most roofing and shingle or sealing problems are not hard to see because it's common sense to spot something that looks like corrosion or water damage. The external part of your roof, the shingle, is the first line of defense from the elements, but there is material underneath that you need to protect and take care of as well. If you're interested in getting a new roof because there's some kind of damage, find out if you really need to replace the entire roof. Check out your roof, and unless you have very visible damage you may be surprised at what you find. Perhaps the best thing is to speak with someone who knows about roofing, and preferably someone you can trust. Sometimes it is frustrating because you have to rely on what others tell you. Any time you are seeking expert advice, you should be ready to pay them something for their time but it will be worth it.
It all depends on where you live of course, and if you're in a hot environment then install some vents - or have your roofing contractor do it for you.
This is especially important if you're in a humid climate, and reducing that hot, humid http://www.roofrestorations-melbourne.com/commercial-roofing/ air below your roof will serve you very well. How about investigating the many types of systems available for venting from the roof, and there are some that are pretty slick. Everything you do will have a cumulative effect, and that's just how it goes with these things. Think twice about hiring any contractor to install your roof because you just have to due some good diligence. If you need to know why this is so important, do research about the importance of finding a trustworthy roof contractor.