The question is, will a robot that is autonomous enough and sophisticated enough to build a house be cheaper to operate than a human worker? As complexity of machines increases, the number of ways they can break down increases exponentially. Humans bodies are self-repairing for the most part except in cases of severe traumatic injury and disease.

The complexity of a robot is mostly in the software. Input (cameras and microphones) and output (robotic arms, etc) have been around for decades, but robots have not been able to interpret a picture of the world effectively. That's a software problem.

The thing about software is that you write it once and then it's free to copy. The first general-purpose robot workers will probably run expensive proprietary software, but 10 years later there will be usable open source versions. The physical robot itself will become cheaper, if anything, due to economies of scale.