Housing Contract Question

My son got a housing contract and we need to pay a deposit. He is debating between rooming with few of his friends at school or find someone through social media. Will be he able to pick his roommate later or should he know at the time of paying deposit?

You can change your preferences up until July 1st. I met my roommate at orientation (mid June) and changed her to my preferred roommate. Hope he get everything figured out!!