I have some storage space in my roof, and I had occasion to go up there one hot day in January. It was 60+ degrees, and I didn't stay long! Since the roof has been painted, I've checked it a few times and the hot day temperature seems to be around 32 to 35. That's a huge difference, and one that I'm mighty glad of.
On most days the house itself peaks at 27, which is very easy to live with. As you know we've had several hot days on the trot recently and by the end of each hot spell the house had reached 31 inside, but it fell each evening when the windows and doors were opened up to catch any breezes. An ordinary fan inside helped the comfort level, as we don't use the old air-conditioning unit that was in the house when I bought it. It would use nearly 5 times the energy that the modern units require.
In my travels around Melbourne I've seen many newly painted roofs, but only one other white one, and SO MANY BLACK ONES. What a SILLY colour to put on a roof in this country. Good colour in Scandinavia, maybe, or Siberia!
So here's another tip: if you are about to consider a roof job, please think about ordering white paint. It looks rather nice, costs no more than any other colour, and has the most amazing cooling effect.