There was no specific reference for measurements, I drew out the main shapes on card before I was happy with them, I gauged the thickness to be about 1" high and made that the height of all my internal support as well as the side walls, same with the ribs, they taper up to 1.5" I think a lot of this has to be decided by you in the end, though I found asking many questions of other guys who have built these helped a great deal