The most I have ever covered was the back, and one of the sides, usually the left.
I cut a very thick sheet of clear plastic the exact size, and duct tape all around.
I would be afraid of not getting proper ventilation covering 3 sides as I want the cage to dry as much as possible between mistings to reduce bacterial growth.
I would maybe cover the back , one side, and half of the other side.
Like a strip of plastic not as wide, leaving a few inches on both sides for venting.