Sometimes a roofing las vegas contractor with his own workers can be more cost effective than a contractor who has no workers. The more people working on the roof, the quicker the job can be completed. A person working alone will often charge the same price, but will work more slowly. Make sure the labor cost is not too high.
Ask the contractor to give you their license and insurance information. If they won't, do not think about hiring them. You won't have any recourse available when they do a bad job which ends up costing you a lot of money to fix.