I decided on kitbashing(+clay sculpting) for the final. I designed a biomechanic model and started from making a skeleton by wires. I scavenged every part from the shop and junk shelf. Most of those were circuit components so that I could make it easy to get a likely-looking mech model.
I attempted to make the model as a halfway action figure, so I used a potentiometer and rotatable disk into a neck and waist parts. I also had to manipulate and reassemble some parts to make a certain weapon or body part.
I got through several trials and re-modelings to make the model can stand and keep balance by every angle.
I sprayed primer on that to prep for painting and dried it as fast as possible by air dryer to prevent the clay drooping. The next step is making three more of this and painting the model with water resists acrylic paints.