The Salatin pen November 2008
The right front quarter we made a bi-fold for ease of access. The diagonal opposite left back quarter we made to raise up to vent, as we'd read these were called "easy bake ovens". It's lined with window screening to keep chickens in when open.
The wheel mechanism is you pull the retaining pin, push the arm down and re-insert the pin. It raises the pen up on the wheels.