Something I wonder about Star Wars

If young Anakin is a poor slave, building a robot with parts that he's scavenged (and probably time that he's scavenged), then why is he building a protocol droid? Wouldn't it be more useful to him to have a robot that could do physical labor, to reduce the amount of work that he and his mother have to do? Or some sort of fighting robot, so he could gain freedom for his mother and himself?