A grand opening will be held Monday for the Mattapan Community Health Center. Local leaders, including Mayor Thomas M. Menino, plan to attend the 11 a.m. ceremony. The center, at 1575 Blue Hill Ave., cost $34 million to build, including $11.55 million in federal stimulus funding. The four-story, 59,000-square-foot facility is more than three times larger than the health center’s current one-story home nearby. It is expected that the center will double its current patient population, which is about 7,500. The new location has more parking and will provide additional services. The ground floor is being rented by Citizens Bank and CVS, the first large pharmacy store in Mattapan Square in more than 30 years, leaders of the center have said. Already among the neighborhood’s largest employers, the center will employ an additional 44 people. More than 200 construction workers built the health center over the past two years.