Can you make a bed canopy?

Yes, you can....several ways. One way is to install a ceiling mount curtain rod around your bed. Depending on the height of the ceiling, you can use ready made flat sheets and use drapery clips to hook to your curtain rod. If they are too long, fold the top over facing outward and iron a very straight crease. Temporarily pin this together until you get your clips on your fabric. This will make a ready-made valance at the top without any sewing. Keep in mind where your ceiling fixture is, or a ceiling fan. Also, doing this can make it hot at night with curtains closed. They were originally designed for large estates several hundred years ago with a four poster bed to do just that in the winter.

You can also add a headboard and a footboard and attach to the frame or rails of your bed. This is much more time intensive and probably more expensive. Someone can probably help you with more details as far as construction and paint or staining.

I have had this corona with curtain for many years . . . in fact just took it down to wash recently. My husband made the wooden "crown" and fastened it to a ceiling joist. A seamstress friend made the curtain. I made the curtain upper border out of napkins.

https://www.youtube.com/watch?v=5opTqLTlIfU

Here's a DIY bed canopy you may want to consider: http://allcraftythings.com/diy-bed-canopy/