Two years after work started on the Austonian, a flag was hoisted to the top of the 683-foot-tall tower Thursday, marking a milestone for the tallest building in Austin. Workers put in the last steel beam that will support a glass crown to be finished in December. The project is the tallest residential building west of Chicago, the builders say. Units are priced from about $500,000 to more than $8 million for a penthouse, with the first residents expected to start moving into their new digs in June.