I have always lived in regions where air conditioning is considered required during the summer. In the US Southwest, temperatures often exceed 100F (40C?) on a daily basis, and there have been deaths when the power blacks out or the A/C fails, mostly the very ill, the elderly, and the extremely young. (All people who have some difficulty with thermal regulation.)
If we make the entire outside surface of the house out of mirrors, including the roof, the house will be distinctly lower in temperature, and thus will require less energy to keep it cool. This is the good side of this plan.
The bad sign is that the immediate outside will be painfully bright. It will literally hurt to look at your new house during the daytime. Oh well.