contractor vs master builder

contractor

noun
  • A person or company that builds or improves buildings. 

  • A person hired to do a job on a business contract, as opposed to a permanent employee. 

  • A person or company that performs specific tasks like electrical or plumbing work in construction projects. 

  • A person or company hired to maintain existing facilities like air conditioning systems, groundskeeping, etc. 

master builder

noun
  • A person who is adept at overseeing the construction a building using the plans drawn by an architect 

How often have the words contractor and master builder occurred in a corpus of books? (source: Google Ngram Viewer )