I did it this way; Painted the ceiling blue (whatever color blue you like) they dabbed some white paint on with a bunched up rag (look at cloud pictures)
I bought some glow in the dark stars and moon at the dollar store and stuck them up there (the tacky tape comes with the stars)
I also painted a tree on one wall and on the branches hung some birdhouses with cup hooks I even found a birds nest that I hot glued in the tree branch . I am no artist, but if I can do it so can you.Give it a try , you can always paint over mistakes
I later found out you can rent a projector from your library and trace a tree that way (too late for me to do)