Can someone help me answer this question please...? Is it possible to think of a building or complex of buildings serving as an organizing metaphor for a contemporary city in the way a cathedral served in the middle ages?

Of course. Carthedrals were the central and unifying element in Medieval society in both practical and symbolic terms.

Practical because the Cathedral was the source of learning,and determined the moral and legal rules of society and was the source of learning as well. Symbolic becuas it repersented the values and beliefs of its citizens.
.As the city surrounding the cathedral or church relied on that institution for it laws and culture, so too do the cities that surround our institutions of learning and law: the schools, univeristies, colleges, and the Civic Centers of government: Town Halls, Courthouses, shopping malls and cultural centers provide that same direction for a city's social and cultural life.