Dream up
Definition 1 of 1
Pro Tip 1/3Creativity Involved
Use 'dream up' when implying the creation involves imagination and originality. 
They dreamed up a whole universe for their science fiction novel.
Pro Tip 2/3Not Always Realistic
'Dream up' can suggest ideas that may be impractical or fantastic. 
He dreamed up a plan to build a castle in the sky.
Pro Tip 3/3Slight Informality
The phrase 'dream up' is casual, more common in informal speech and creative contexts. 
Let's dream up a fun theme for the party!