I am not arguing that I can dream up any reality I like. - John Louis Lucaites, Celeste Michelle Condit, Sally Caudill: Contemporary Rhetorical Theory.
devise or invent; "He thought up a plan to get rich quickly"; "no-one had ever thought of such a clever piece of software"
If you dream up a plan or idea, you work it out or create it in your mind. I dreamed up a plan to solve both problems at once His son hadn't dreamed it up
[ 'drEm ] (noun.) 13th century. Middle English dreem, from Old English drEam noise, joy, and Old Norse draumr dream; akin to Old High German troum dream.