Going from complete ignorance about what all is needed for a successful roofing job to learning something is basically what you need to do. A huge part of getting the result you want is planning, and it starts right from the very beginning. Your list of what needs to happen should have priorities on it for the things that are a little more important than others. All contractors (in the US) are regulated to some extent, and at least all your state and find out if there are any official complaints about the contractor you’re dealing with.

Evaluating the Damage
One thing about getting a new roof is to know if there are any problems that need to be fixed now or along the way. If you find something wrong, then obviously this will need attention at some point before your new roof is done.
You have to ask yourself just exactly when you want to know about it. You also want the work to keep going from start to finish, and you may have weather considerations to think about as well. Actually, it’s a good plan to add a little more to your projected budget for anything unforeseen. There are all kinds of different situations in which the homeowner thinks a new roof is needed. It’s hard to speculate, and you just need to assess your roof. Most of the time a contractor will tell you to do an entire roof – but that is not anything shocking. Sometimes it is frustrating because you have to rely on what others tell you. Just like with a doctor, you can get second opinions and then just weigh what they all tell you.
Structural Integrity
Roofs that are losing their structural integrity is a sure sign that intervention needs to happen. Obviously if the roof line is sagging, then have your roofing contractor come out and assess the situation. It’s always hard to tell exactly what’s going on unless there is obvious damage. Depending on the exact cause for the sagging, you may be able to get away with adding more support beams in the attic.
The last thing you want with a new roof installation is to have a serious problem occur. Sometimes the unforeseen can occur, and you just deal with it as it happens. And your best defense is knowledge and information and that’s it. And do pay attention to what is being done each day, but it’s really not necessary to camp out on the lawn.