One of the best reflectors is magnesium oxide. When a test
instrument is used it's magnesium oxide which is used to
reflect light.

Nearly any materials absorb after you get past the red color
into infrared and only things like gold or well polished
aluminum will reflect heat without absorbing heat itself.

It's hard to make a good heat reflector from even a polished
sheet.

I don't know any specs for paint but from my experience I
believe you will find that bright white paint is the best
for all round use for even reflecting heat.

Otherwise consider using a new material which is simply
aluminum deposited on a plastic base. It's unique because
for $2.00 / sq foot it can withstand 10+ years of direct
sun with only clean water rinsing.

If you're interested in the product that I know of reply
and I'll go looking for it.

Regards,
Andre

I believe in proper attic and roof ventilation that sucks the warm air out in summer, and a good heat insulation for the whole year.

http://www.greenbuildingadvisor.com/blogs/dept/musings/insulating-pain t-merchants-dupe-gullible-homeowners