Gable fan vs Roof fan
Both of these two fans are installed in the attic and ventilate it. By ventilation, the temperature is reduced, and it can reduce wear and energy costs.
Gable fans are made in larger sizes than roof fans, thus having an advantage on the cooling capacity.
Newer roof fans have solar panels to draw their electricity. Gable fans can also use solar power, but they are less efficient as they receive less sun exposure.
Installation and maintenance
Gable fans are more difficult to install, unless there is already a gable vent in place.