Simplest molding casting material and also tutorial to make your own mech plamos? I'd say plaster of paris for mold, OR even design, and the plasticine for mold, Also Or, design, but plasticine is very oily, and plasters are, brittle? that the word? not sure any other alternative, for starter, if you want to "sculpt" with any of those, theres not much general guideline, so, T&E all the way to infinity,infinite deadlines like your lil own bosses, regardless if, you have a boss at the moment.