A person who builds machines is typically called an engineer, mechanic, machinist, or inventor, depending on the context and their specific role. Here's a breakdown of these terms:

1. Engineer:
   An engineer is someone who designs, builds, or maintains machines, systems, or structures. They often apply scientific and mathematical principles to create functional and efficient machines. Engineers can specialize in various fields, such as mechanical engineering, electrical engineering, or robotics. For example, a mechanical engineer might design a car engine, while a robotics engineer could build a robotic arm.

2. Mechanic:
   A mechanic is someone who repairs or assembles machines, particularly vehicles or mechanical systems. While they may not design machines from scratch, they have the technical skills to build, maintain, and troubleshoot them. For instance, an automotive mechanic builds and repairs car engines.

3. Machinist:
   A machinist is a skilled worker who operates machine tools to create or modify parts for machines. They often work with metal or other materials to produce precise components that are essential for building machines. Machinists are crucial in manufacturing industries.

4. Inventor:
   An inventor is someone who creates new machines or devices, often through innovation and experimentation. Inventors are known for their creativity and ability to solve problems by designing entirely new machines or improving existing ones. For example, Thomas Edison is famous for inventing the light bulb and phonograph.

5. Technician:
   A technician is someone who assists in building, installing, or maintaining machines. They often work under the guidance of engineers or scientists and focus on the practical aspects of machine construction. For example, a computer technician might assemble and repair computer hardware.

6. Robotics Specialist:
   If the machines being built are robots, the person might be called a robotics specialist or roboticist. These professionals focus on designing, building, and programming robots for various applications, from industrial automation to medical devices.

7. Tinkerer:
   A tinkerer is someone who enjoys building or modifying machines as a hobby. They may not have formal training but are skilled at working with their hands and experimenting with mechanical systems.

In summary, the term used depends on the person's expertise, the type of machine being built, and the context. For example, if someone is building a complex machine like a spacecraft, they would likely be called an aerospace engineer. If they're assembling a simple mechanical device, they might be referred to as a mechanic or machinist.