Hi, Susan, I can't tell you how to apply your copper roof without seeing it. Usually, these have standing seams which take special tools to bend, but there are many variations. After the roof is fitted, you will probably want to secure it with nails somewhere around the bottom and they must be copper nails. Dissimilar metals corrode easily in a wet environment.
If you can get any information on the cupola or the roof's manufacturer, you should certainly try to contact them. With this being a "high end" piece, you want to put it together correctly and make it last as long as possible. So if you can make contact with the originator, they should be able to give you some direction.