Roos spent his youth with a wide variety of Dutch clubs, before earning a contract at English Conference Premier side Nuneaton Town in November 2013, and gained a lot of attention from clubs throughout England with his performances during a run of clean sheets.

He was sold on to Derby County in January 2014, and made his first-team debut for the club nine months later. He was later loaned to Rotherham United, AFC Wimbledon, Bristol Rovers, Port Vale and Plymouth Argyle. He broke into the Derby first-team in January 2019. Roos left Derby at the end of the 2021–22 season and signed for Scottish club Aberdeen.