In the United States and Canada, they're often referred to as roofing contractors or roofing professionals. The most common roofing material in the United States is asphalt shingles. In the past, 3-tab shingles were used; nowadays, "architectural" or "dimensional" shingles are becoming very popular.
A more recent design is the installation of a roof deck with foil-backed foam along with a second deck that is air-gapped away from the foil-backed foam to allow air to flow vertically to a ventilation outlet at the peak of the roof—it is a double deck design with an air gap. This design improves efficiency.
Condensation within the roof space is much more of a problem today due to: much less fortuitous ventilation due to tighter building envelopes with high performance windows and door and no chimneys leading. This tighter envelope means the air temperature in buildings has risen, the warmer the air in the building is, the more water vapour the air can carry.
A person that specializes in roof construction is called a roofer.