Normally, you would add the cornice over the curtain rod. The purpose is to conceal the rod and give a finished look. You can build from wood and upholster, styro foam, wood without upholstery, or foam board. Here are a collection of projects for you to look at, hopefully one of them will be something that you like.
My diy upholstered cornice treatments are mounted on wooden boards. Sometimes foam sheets can also be used
Here's a cornice with an attached round curtain rod so you can slide the curtains back and forth.
Here's another tutorial on building a cornice box with an attached curtain rod: http://www.fromthesehands.net/tutorials/2010/7/27/cornice-board.html
How to build a wood cornice box with attached curtain rod
A Cornice is a hard top covering over your window that is fabric covered. You could make one out of wood, styrofoam and even particle board (cardboard maybe). The entire cornice would be stiff though and it is upholstered. A pelmet is a stiff flat valance that hangs. Usually it has crinoline, buckram or a stiffener Is used to give a feeling of a cornice but softer since it is hanging. A valance is probably what you are thinking of. That is what you would use to hang on a curtain rod. It is similar to a pelmet but has pleats and flows like a swag or multiple swags in different variations. If you want to make a valance that hangs on a curtain rod you can certainly make one that is flat. Here is one that is easy:
Hi Linda, hope this is the information you are looking for to make your cornice using a curtain rod. Good luck with your project. How to Build a Wood Cornice Box with Attached Curtain Rod
livelaughrowe.com › build-wood-cornice-box-attached-curtain-rod
Jan 13, 2015 - Yesterday I shared my new (and fabulous) curtains in my breakfast room. Today I'm back to share how to build a wood cornice with attached ...
Here's a post that might help - https://livelaughrowe.com/build-wood-cornice-box-attached-curtain-rod/
Hi there, you can purchase curtain rods with a long L bend at either end that you could then mount at the top of the window, that would create the look of a cornice without having to build anything. A short curtain would then wrap all the way around it.
Hi Linda, here is one more type to check out, it give instruction, hope it helps you
In room interiors, the cornice is the decorative wood or plaster molding, a surface with raised designs (sometimes made of plaster, hence the name molding) that circles a room right below the ceiling. What are you attempting to do with a curtain rod? Two very different things.
This is a good DIY. https://www.familyhandyman.com/carpentry/how-to-build-window-cornices/
Could not find one made with a curtain rod but found this https://www.familyhandyman.com/carpentry/how-to-build-window-cornices/