Unless you have really good insulation, in hotter areas, your roof will absorb a lot of heat and that gets transferred to the attic and then to the rest of the house. One of the cheapest and best upgrades in hotter areas is to have an attic fan and vents to send the hot attic air outside.
> attic fan
The cupola does that using the "stack effect" and the acceleration of the wind as it hits the sloping roof, at zero cost!
That said, I do have an attic fan connected to a thermostat. I'd rather have a cupola, though.