Maurice de Sully came from a poor family at Sully sur Loire, was educated in the schools of Paris, and became bishop of that city in 1160. Contemporaries remarked on the origin, which tells you it was unusual: a twelfth century bishopric normally went to a man with land and relatives. What made another route possible was the schools themselves. Paris in that generation had become the place where theology was studied at the highest level, teaching drew students from across Latin Europe, and a reputation made in the classroom could be converted into office. The university that grew out of those schools was still decades away from a formal existence.
His most widely copied work was not a building. He composed a cycle of model sermons in French, one for each Sunday and feast, short and plain, written to be used by parish priests who had neither the Latin nor the training to compose their own. Manuscripts of them survive in large numbers and in more than one language. That is a serious act of religious policy: it accepts that the ordinary clergy will preach badly or not at all unless someone supplies the words, and it puts the effort into the vernacular where the congregation is.
The model sermons also tell you what was assumed about a congregation. They are short, they retell the gospel of the day and then draw a plain moral, and they do not argue. Preaching of that kind was the main channel by which doctrine reached people who could not read, so a bishop who wrote the scripts was making a decision about what the ordinary Christian of his diocese would and would not be told.