Be mindful that a job site is hazardous and keep clear as much as possible.
Do make sure that the materials you are paying for are used on your roof. These materials include starter shingles along the edge of the roof and up the rake. You have to have felt paper covering the whole house. Ice and Water protection must be in the valleys, some companies use metal and others use rubber type membrane. Something has to be in the valley. Drip edge also has to be used on every edge on your home. Flashing (small pieces of metal) has to be used.
Do ask for references and call and check out the company. Make sure they are licensed and insured. Is the company going to be there if you have a problem.
Do make sure that you are having ridge cap put on your ridge.
Don't allow the contractor to bully you into not looking at the work being done on your home or business. And if they can't answer a few questions about what they doing you should ask yourself if you choose the right company.
Don't allow children to play around the site there is always the chance something could fall and injure someone. On business sites we put out orange cones to keep people coming into your office aware work is being done. We do everything possible to ensure every ones safety.
Don't let yourself be talked into taking shortcuts that will cost you more in the long run. Having felt paper, starter shingles, drip edge, ice and water, flashing and caulk is a must on all jobs. (Except some flat roof systems) If these things are missing you will pay later for new decking, new fascia etc. This is not a you might this is a you will . We cannot say enough that your roof is your most important investment in your home or business. Make sure you are getting a good job.
Don't be afraid to ask for these things, it is your right as the homeowner, business owner or commercial contractor.
Don't allow seconds and defective shingles to be used on your roof. Defective shingles don't have warranties.