The see to which William appointed his half-brother Odo. It had become common place for the dukes of Normandy to appoint kinsmen to ecclesiastical positions.
It is entirely possible, however, that this move would have displeased some members of the Norman clergy, such as the renowned scholar Lanfranc of Pavia, who denounced simony (the selling of religious offices).
Indeed, Pope Leo IX convened the Council of Rheims in 1049 to deal with just such issues. Shortly after the council, Archbishop Robert of Rouen, William's uncle was deposed. The two events may be coincidences, as Odo was appointed bishop of Bayeux at around the same time. However, it is noteworthy that Robert's successor was a candidate from Rome.
The construction of the cathedral was started by Odo predecessor, Hugues II, and finished in Odo's lifetime, though there are later additions.
One noticeable later addition is the story of the martyrdom of Thomas Becket of Canterbury, during the reign of William's great-grandson, Henry II of England.