In some of the more traditional denominations - certainly Catholicism and Anglicanism, to name two - churches or church buildings are named after "saints". This is in contrast to the more evangelical denominations, where churches are generally either named after their local area ("Mytown Baptist Church" / "Mytown Methodist Church" etc.) or more free-form.
How do the traditional churches determine which saints to dedicate each congregation/building to? Is it the building or the church itself (the people) that take on the name?