Unfortunately, projects like these are where "makers" and engineers part ways. It's the boring bits of engineering that always get people: costs, safety standards, and scalability. In this case, for example, where does the foundation for the house come from? You can't 3D print it. You need an earth mover or a bunch of Mexicans with shovels to dig it out. Ok there goes one of your biggest costs. Now on to printing your house. Concrete is pricey even before you create a fancy mix design that can be extruded and not slump. Any cost savings here? probably not. Now your house needs a roof. Well, if you can't print overcuts with plastic you're not doing it with concrete, so a standard truss it is. Again, no cost savings. If you've got this far, you haven't saved any money and we don't even know if your house will pass structural/safety muster. I hate to be a downer, but a lot of these idea are just bad. If you want cheap construction, we'll have to look elsewhere.