For the eye, get some brass or aluminium tube from a model shop, cut off a 1mm ring then push it unto some greenstuff/similar putty. The putty will form a dome/lens shape inside the ring. Wait for it to dry then trim off the back of it and glue it over one of his eyes. Fill the gaps with more putty.
EDIT: To cut brass/aluminium tube, take a stanley knife or other heavyduty modelling knife and simply roll the tube gently back and forth on a flat surface using the blade. It prevents distorting the shape of the tube as you cut it.
For the leg, just add some plastic rod supports or pistons and some armour plates.
Maybe add a small stove-like device to his back with a chimney. Paint any grooves in the door a sickly green to show it uses warpstone laced coal to power him.