Cloud base and Cloud ceiling.
Cloud base is the height of any cloud above the ground or water. Ceiling refers to the lowest level of cloud base which covers more than 50% of the sky.
The use of the preposition 'cloud' before ceiling may be confusing matters, it may be easier to think of aerodrome ceiling or route ceiling.
If you are referring to the vertical extent of the clouds above their bases, they are generally referred to as tops.
So you could have few (1-2 oktas) cumulus with bases of 3000ft with a high level cirrostratus at 15000 feet. In this instance the cloud base of the Cu would be 3000ft but the ceiling would be 15000ft. The tops of the Cs may be 17000 ft.
Hope this helps.