Hi Missy! What would you like to do? Build one?
I would recommend first mounting a floating shelf, with an edge or lip to prevent frames from slipping off. That way, you can switch out individual pictures any time without having to make any more holes in the wall. The hardware on floating shelves is hidden inside, which helps to feature what is in the frames, not the hardware, when you look at the shelf.
Make sure it's high enough that you can't hit it when getting up off the couch
Be careful that the shelves are not in the way of someone sitting down on the couch. Had some over my bed one time and felt they were going to fall. If the shelves were not deep it wold be fine, I would think.
Ikea has awesome picture rails that are affordable and vary in size: