Complex sentence: The Bishop of Exeter, John Grandisson had founded a new church at Ottery St Mary, which William Joy had built, and in 1342 he was in put charge of works at Exeter Cathedral.
Split into simpler sentences: The Bishop of Exeter, John Grandisson, founded a new church at Ottery St Mary, which was built William Joy. In 1342 he was in put charge of works at Exeter Cathedral.