What does Buddhism say about having dreams about the Buddha?
The dreams Bodhisatta had about his future Buddhahoood are given in the Supina Sutta.


  "When the Tathagata — worthy &amp; rightly self-awakened — was still just
  an unawakened bodhisatta, five great dreams appeared to him. Which
  five?
  
  "When the Tathagata — worthy &amp; rightly self-awakened — was still just
  an unawakened bodhisatta, this great earth was his great bed. The
  Himalayas, king of mountains, was his pillow. His left hand rested in
  the eastern sea, his right hand in the western sea, and both feet in
  the southern sea. When the Tathagata — worthy &amp; rightly self-awakened
  — was still just an unawakened bodhisatta, this was the first great
  dream that appeared to him....


You might also be interested in knowing the meanings of the dreams, queen Maya(mother of the Bodhisatta) saw.