Here's why:
* Active Voice: The subject of the sentence performs the action. It follows the pattern: Subject + Verb + Object.
* Passive Voice: The subject is acted upon. It follows the pattern: Object + Verb (to be) + Past Participle + by (agent).
The sentence lacks a clear subject and object. It's unclear who "their own" refers to and what they built the house with.
To make it active, you need to provide a subject who performed the action of building the house. For example:
* John and Kate built a house with their own hands. (Active voice)