I used the pull out devices that IKEA supplied with the modular units.
The two galvanized steel sliders are tubular, about 3/4” by 1” if I remember, designed something like a rail inside a sliding C channel. The rail screws into the sides of the adjoining cabinetry while the slide out shelf clips to the top of the moving channel.
Understand what I mean?
The desk is at a good work high when I am sitting opposite on a slightly pulled out bed.