Seeing as though we are making a robot let's change the material to a metal shader. You can set a material for each model per layer so you will have to choose each layer and adjust it to suit. To do this make sure you are on the Layer menu again, then select the part you wish to change the material of. With the layer selected, press the green settings button on your Tool hand. On this menu change the material by clicking Metal at the top middle. Now you can change the roughness, diffuse settings and the occlusion of the material.