A roof vent installation company will charge an average of $350 for the installation of roof vents in Charlestown and the cost will already include the materials needed and the labor. If you do it yourself, you can pocket up to 65% in savings but this is assuming you already have carpentry experience. Otherwise, it will be in your best interests if you just hire an installation company instead. If you have a steep roof, the installation will be much harder which means it is another reason for you to hire a professional unless you want to put yourself in danger.