Construction of the major new distribution center for Sysco is progressing on schedule, and the company has begun adding employees, according to Selectmen Chairman John Henry. “They’re booming right along,” said Henry, who said he stopped by a week ago and watched part of the installation of about 15 acres of roofing on the roughly 650,000-square-foot building. He said the company expects to meet its target opening date of early June. “It’s gone very, very fast,” Henry said, adding that the company announced its plans for construction at the Plympton Industrial Park a little over a year ago. The plant will employ about 800 people, most of whom will be transferred from Sysco’s current facility in Norton. More information about the company is available at syscobostonllc.com.