Welcome Mike:
Yes, there is a heat tape for roofs. Check with the local heating and air conditioning supply house. Here is a site that tells about it.
http://www.deanbennett.com
The heat tape in this site is self-regulating; that is, if an area of the tape gets too cold it will heat up, when it is warm enough it will shut down. It can even be crossed over itself with no danger, it won't melt down or short out.
Glenn