K.C. McKillip is brewing up a keg full of ideas for the former Gerretsen Building Supply retail store and warehouse in Roseburg. His first idea is to open the Backside Brewing Company with partner Ben Looney at the 1640 N.E. Odell St. site. Their target date for selling Backside’s first bottle of beer is July 4, 2013. Beyond that, McKillip’s ideas for the 18,000 square foot space, for which he has a lease-to-buy option, include a tasting room for the brewery, common and individual work spaces for other small manufacturing, industrial or food processing businesses and a pub or small …