Advice about rooftop greenhouses

[Carl Johnson]

Dear Everyone,
        My university is planning to build a new building for the Biology
department, and the current plan is to place the greenhouse on the roof of
the new building. Because the greenhouse for our current building is on the
ground, we don't have any experience with rooftop greenhouses, but I expect
that there can be serious problems with light intensity and heat,
especially in the Southeastern USA--we are located in Nashville, Tennessee,
and the summers are very hot and humid.
        We would appreciate it if those of you with experience of designing
rooftop greenhouses could advise us, especially those of you from the
Southeast. What are the major problems that need to be considered? Can
anyone recommend a good architectural firm with experience in designing
rooftop greenhouses that could be consulted?
        Thank you!
                Carl Johnson
                Vanderbilt University