Part of finding the best location for an elevator is to make sure there are no major obstacles on the roof. It is generally required in order to meet safety clearances above the elevator cab that the roof is raised in the area above the elevator shaft.
It is simply a structural challenge assuming that the ideal location chosen by your design-build professional does not have a rooftop unit and related duct work or other major obstacles . Often the new shaft walls will support the roof around the new opening or perhaps some added columns and beams may be needed.
Every building is different as some roofs are supported by bar joists and steel decking, where others are precast concrete and still others are framed with wood joists, beams and wooded decking.
Each situation would require a difference structural answer depending on the existing structure and existing loads on that structure. You may rely on your local design-build general contractor for answers to these questions.
