lean-to vs roofing

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. 

roofing

noun
  • A way of travel which consists in clambering over the roofs of skyscrapers. 

  • The process of constructing a roof or roofs. 

  • Material used on the outside of a roof, such as shingles. 

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