Don’t have decent stone or a good supply of metal? The resourceful wizard uses whatever they have to hand including junk and refuse. Garbage golems are held together by their incantations alone as their constituent parts of rotting matter and broken structure aren’t secure by themselves. The poor quality of the ingredients greatly limits the will and thought of the golem, limiting it to the simplest of tasks and instructions. Their only real advantage is that they can easily find material to self-repair.