gazebo vs summerhouse

gazebo

noun
  • A belvedere, either a type of summer-house or a roofed, detached porch-like structure, usually in a yard, park or lawn. 

summerhouse

noun
  • An outbuilding in a garden where the owners can relax in warm weather. 

  • A house owned not as a primary residence and used as vacation home during warm weather months of the year. 

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