The Ruhl Building, a handsome Main Street building 115 years young, has been purchased by an investor who plans to put apartments on the two upper floors.Market-rate apartments, by the way. Depending on when Taj Khan gets ’er done, that could be a first for downtown Stockton’s revival.“When I looked at it, I just kind of fell in love with it,” said Khan, a Lodi resident and former San Joaquin Delta College trustee.