If you are new to robotics I suggest getting some ready to use parts like an Animatronic Head Kit. But if you want to build everything from scratch I recommend checking out the How to Make a Robot tutorial series, as well as the Robots section where you can find some cool animatronics that were made by community members. For example
If you want the eyes and the mouth to move like the first one you will need some servos and you could take that tutorial as a guide and use aluminium sheets for the structure of the head too but there are other materials you could use as well like cardboard, wood, plastic or maybe you want to 3D print it, it’s totally up to you (but maybe this tutorial might help you out with the choice). You could also check the Ultimate Guide to DIY Animatronics by Steve Koci.