Here we will list some of the plastic/metal other parts to build a humanoid, animal or other type of robot.
Your frame and covering for a vehicular or walking robot could be light plastic, durable pvc, UHMWPE, or mylar or some light metal like sheet metal, titanium, or materials like steel, kevlar, fiberglass.
Brackets are needed to hold servos and some type of brackets are used for joints (neck/shoulder/arm-hand/hip, leg-shin-foot-toes-heel)
Attachment choices- nuts and bolts of varying sizes or screws or glue
Springs are often used on humanoids or animal robots to reduce the strain on a servo (on legs/arms/head).
If the humanoid robot is heavy then you must choose the right components to support it. On a strong base or legs that are sturdy and won’t collapse.
Also you must ensure that when the robot falls or is hit that it would shatter into pieces. The servos need to be protected from the elements if it is used outside.