Rojas was born in New York City on February 23, 1963, and grew up in Red Hook, Brooklyn. His early influences included Eddie Palmieri, Willie Colón, and uncles who played percussion and trombone. He began on trombone at elementary school, then changed to tuba in junior high school. At age 15, Rojas began lessons with tubist Samuel Pilafian. He went on to attend the High School of Music & Art in New York, and studied further at the New England Conservatory.