The top view is the frame for the shelf from 1X3 clear pine. Cover it with 3/8 ply good one side. You will need to cut a piece of 1X3 pine to act as a stop see the side view.

The side view shows the track from 1/2 inch ply and the five roller blade wheels or skateboard wheels. The one top wheel and the four bottom wheels sandwich the shelf frame and ply cover. At the left side you will see the short 1X3 that will stop the shelf when its extended against the top wheel. The top wheels have to be placed so the end of the shelf is still supported by the second last wheel.

The end views give you the orientation of the wheels and the 1/2 ply side rail with the shelf sandwiched between the wheels.

Hope this helps.

Dennis