lean-to vs rooftop

lean-to

noun
  • A shelter with a sloped roof; also a building with a similar construction attached to the side of a building as an extension. 

rooftop

noun
  • The area atop a roof. 

  • The top layer of a roof; the material covering or composing a roof. 

How often have the words lean-to and rooftop occurred in a corpus of books? (source: Google Ngram Viewer )