This can help keep your house colder in the summer and can also help prevent patios or garages from heating up like ovens on a sunny day. This can make things more comfortable for you without using the air conditioner and therefore it should also reduce your energy bill. With careful research on your area you can find out if this is likely to save you money and in some instances its virtually guaranteed to be nothing but a benefit.
It turns out they may not be the greatest thing ever as it has been found that it can also dramatically increase your winter heating bill and this depends entirely on were you live. In hotter country's this is pretty obviously a good idea and in colder countries its pretty obviously a bad idea but it can be hard to tell if you will save money or not by having one of these roofs if you live in non extreme weather. The environmental impact is also questionable as the heat being reflected may actually exacerbate climate change.