This is a lock for a bifold door. You open a leaf of the door to slide it over the top of the door. Then you can close the door, and slide this over the two door panels. Essentially this is just a piece of U channel, but I also added an extrusion to the side to act as a stiffener against the forces that will be applied by the door. I also built in support. I recommend making it solid out of ABS for strength.