Flat designed and built as such.

A self-contained flat, part of a larger complex, all sharing a common entrance.

A flat in a building which was specifically designed to be a flat when it was first built.

flat designed and build as such; a self contained residential unit contained within a larger structure containing several self contained units or flats all sharing a common entrance.

A flat designed and built as a self contained residential unit within a larger structure all sharing a common entrance.