build castles in Spain

To create dreams, hopes, or plans that are impossible, unrealistic, or have very little chance of succeeding. You need sound financial advice and a strong plan if you're going to start your own business—don't just build castles in Spain. He keeps talking about how he'll move to Los Angeles to be a famous actor, but he's just building castles in Spain if you ask me. Would you stop building castles in Spain and getting everyone's hopes up? The odds of that billionaire investing in our little company are slim!