California is going thru its worst drought in record. When its over 100 deg you run from the blazing sun to the coolness of the shade. Now imagine your dark asphalt roof ! All the heat is being absorbed into your house. This is what creates the Urban Heat Island Effect. The first option, and cheapest, is to paint roof white to reflect sun and its heat. Another option is my Begent Design Cool Roof.
In the desert shade from the sun is key. Keeping shade in mind I use a local material that is fairly inexpensive and also a good reflector of light. Corrugated steel is used widely in rural areas. In Australia its become a norm in residential and commercial buildings. From the diagram you can the principle effect of this design. By allowing air to move between the steel and shingles , a draft is created as the hot air rises. This chimney effect draws cooler air from below. This cool air is created from the side of house where the steel turn down making a shaded area or void.The top or ridge of roof is left open to create a draft or chimney effect that sucks cooler air from below up and thru roof helping to keep inside temps even thru out the day.
For the ventilation. 2 x4 lumber is drilled with 3/4 inch holes then attached to roof. These creates the void for hot air to rise evenly over roof and out thru the top.
Next the vertical wall support was built and painted as this will be seen from inside house looking out windows.
At the time of writing this the Cool Roof has been up for a month and the results are good. House stays cooler inside considerably longer then before. Looks great to I have to say.