Dad should have been a plumber instead of an electrician, because he is an expert at pipe dreams. He has a lot of big plans, like building a majestic palace for his family called the Glass Castle. Here's his plan for building the Glass Castle, a self-sustaining palace that the family will live in: 1) Build "The Prospector," a machine that will pan for gold. 2) Get rich. 3) ???? 4) Voilà, the Glass Castle is finished.
You can see the holes in this plan—the main hole being that Dad has no drive to ever get a job done. In fact, it's Brian and Jeannette who have to take the first step toward getting anything done: they literally dig a hole for the foundation of the Glass Castle.
What does Dad do with this hole? He dumps garbage in it. Thanks for nothing, Dad.
That's a big ol' metaphor, ladies and gents. Just as the foundation of the Glass Castle is filled with trash, so is the foundation of the Walls family trash. The family's foundation is unstable, and it stinks. It's no surprise when Jeannette, before leaving for New York, tells it like it is to her dad: "You'll never build the Glass Castle" (3.26.31).
The Glass Castle is ultimately the ideal childhood that Jeannette never had. She can't go back in time and build it, but she can write her memoir and make the best out of the childhood she did have.