This is a great question which has some answers in an ABC news article here
The article completed research on the temperature of houses with dark roofs compared to those with light roofs with the difference of 10 degrees in some studies. It also estimated a cost saving of up to $700 per year on electricity by having a light coloured roof.
From personal experience I agree with the cooling effect of a light coloured roof. Especially important in Australia during the summer months. Having lived in houses with different roofs – Old Colorbond, red roof tiles and light coloured Colorbond I can feel the difference in summer. Living next to a house with a dark coloured roof who has the air conditioning running constantly, by comparison, we very rarely use the air conditioning in summer.
Other articles I have read asked the question of home builders why they chose a dark coloured roof? Some have said for the look, others for the lower cost that the project builder offered, and some didn’t realise a dark roof increased the inside temperature.
If you’re building a new home, do some research and comparisons of adding a light coloured roof rather than a dark roof. Using less air conditioning is great for the environment, and better for your wallet when the electricity bill comes in.