U.S. Under-20 Men’s National Team head coach Tab Ramos completed the team’s 20-player roster with the addition of midfielder Dillon Serna as the group prepares for the 2013 CONCACAF U-20 Championship that starts on Feb. 18 in Puebla, Mexico. The Brighton, Colo., native was signed by Major League Soccer’s Colorado Rapids as a homegrown player after being part of the club’s U-15/16 and U-17/18 U.S. Soccer Development Academy teams. Serna played in