I hadn't heard of anyone making their own soy sauce. It's just so convenient to buy the sauce at the local health food store. Some conventional soy sauces contain MSG and sugar. Good alternatives to the conventional are 'Nama Shoyu' and Bragg's amino liquid.
Lovely idea - "Texas Soya Sauce" - we make it in Viet Nam - this article is pretty close to a recipe - www.chubbyhubby.net/2006/03/iffa-homemade-soy-sauce.html Read up about it in Wikipedia also - en.wikipedia.org/wiki/Soy_sauce