Yes, you are correct. Piggy thinks it is best to build shelters on the beach as soon as they crash. He is one of the most rational characters of the book. Keep in mind that the also thought of using the conch as a horn to get the boys together. In view of the characterization of Piggy by Golding, it is clear that Golding views Piggy's rational side as positive.
When it comes to building shelters, it is clear that this a good plan for two reasons.
First, the boys do not know how long a rescue will be. Hence, they would need shelters. And even if they are rescued soon, it is good for the boy to do something productive and work towards a goal.
Second, if there is no rescue for a while, they will need to have shelter or they will not be able to survive. As we all know, shelter is a basic need for life. And if they wait too long, it might be too late.