Robots have been a time-honored tradition of science fiction since early in the genre’s history. They vary wildly from source to source, offering a huge array of options in terms of looks, attitude and human-like characteristics. Before designing your robot, give plenty of thought to how it functions and the general aesthetic of your setting. With that in mind, start to build.
When you draw a humanoid robot, the metal frame has to compensate for the work the bones would do in a regular human. Try sketching a human skeleton side-by-side with a mechanical frame to get a feel for how the metal parts will interconnect.