I took an old door, cut it in half and proceded to make a corner shelf out of it. I started stripping it, but the wife wanted to leave it looking primitive.
I joined the two halves to 2x2 with pocket screws, of course.
Here's the topmost shelf. You can see the crown molding I put around the top, just to give it a little flavor. Notice the pocket screw into the 2x2 at the apex. Since the door panel was too thin for pocket screws I put 3 screws through the back into the shelf.
The hardware was left in its partially stripped state. I took the outside parts of the door handle off and epoxied the inside piece to keep it in place. I put a 2-1/2" piece of edge banding on the bottom shelf as it is about 2 inches above the bottom of the door. This gives it a 3-point support on the floor. Oh yes, the wife changed her mind and decided to paint the finished shelf.