Some Roseburg residents envision a downtown plaza as a place for live music and a farmers market, while others fear the space would be a magnet for the homeless. About 60 people attended an open house Wednesday at the Public Safety Building on Douglas Avenue to discuss creating a plaza. Participants looked at maps, talked with consultants and covered white boards with adhesive notes to give their ideas. The open house was part of a study being conducted for the city by the Portland architectural firm, Sera, which is studying potential sites. Stephanie Newman offered a fresh perspective. She moved …