When you want to add some ventilation to a roof, then you might consider installing round soffit vents or continuous soffit vents. These are both used to allow condensation and moisture to escape from the attic, and to prevent the roof from overheating during the summer. Both round soffit vents and continuous soffit vents have advantages and disadvantages.
Round Soffit Vents
These types of vents are not the most aerodynamic, and they are not the most powerful, so whether you fit these can depend upon the size of your attic space. On the plus side, the round soffit vents are easier to install than other varieties, and you may be able to install these yourself rather than having to employ someone to do the work. They are also widely available, making them cheaper than other soffit brands.
Continuous Soffit Vents
These types of vents are often used when the roof has more than usually narrow eaves, or if the attic insulation has to be fully vented. The continuous soffit vent is suitable when the eaves are less than 16 inches wide, but you will need to have assistance in fitting them. They can also be very expensive, which can make them prohibitively costly.