Hello I am trying to make warhammer 40k molds with plaster does anyone know of easier methods for making them?

I have been trying this all day using multiple methods i have found on the internet but none are really for making warhammer models... I have a metal chaos terminator without arms a head or trophy rack and i decided why not i could probably make a few more parts if i get the body right I have heard that this is illegal but i am NOT selling them so i dont think it is... any help would be nice. (In my mind GW overprices their models way too much).