Ceiling : (noun)
1 ) Top inner surface of a room "Do not bump your head on the low ceiling."
2 ) Maximum altitude at which a particular aircraft can normally fly "It is an aircraft with a ceiling of 18,000 feet."
3 ) Upper limit "There is a ceiling on business rate increase."
Roof : (noun)
1 ) Structure covering or forming the top of a building, vehicle, etc… "This is a house with a slate roof." "How can you live under the same roof as that woman?"