You could make a bed canopy but use shower curtains in place of material. Here is a link with helpful ideas:
What a great idea! You can get shower curtains in almost any design, too. You could use solid color curtains to expose the “sky”, and add a curtain of a famous landscape painting to fill the wall above the bed. The Smithsonian Institute and Wish.com are great sources. Ooh, I can see a giant Mona Lisa stapled to your wall, now.
if you have some sort of wood headboard, or if you can cut the shape you want out of foam board, padding it is simple. I would work on the floor, or on a large table, but you could also make the headboard on your wall. Buy a roll of quilt batting. Cut pieces of the batting the same size of your headboard. Staple along the sides and throughout the middle. Add a second layer if you want a fuller look. Then use the shower curtain for the top layer. (You could use plastic tablecloths, but they are not as thick and durable.) Staple the curtain in place, pretty tightly, stapling to the back of the headboard if you can. You have so many options, and you don’t have to spend much money for a unique bedroom treatment. Shower curtain liners and plastic tablecloths could make cute window curtains and pillows. Sew, staple, or tie the “fabric” as you wish. Best wishes, Jewell!