build castles in the air vs make-believe

build castles in the air

verb
  • To have any desire, idea, or plan that is unlikely to be realized; to imagine visionary projects or schemes; to have an idle fancy or a pipe dream; to daydream. 

make-believe

noun
  • The quality or act of pretending; acting as if something is true when in fact one knows it is not. 

  • The action of pretending or imagining that things are better than they really are. 

How often have the words build castles in the air and make-believe occurred in a corpus of books? (source: Google Ngram Viewer )