With the first half of the bike-friendly G12 development scheduled to begin construction later this year, it's time to take a look at 12th & Olive, the second phase of the $245 million project.  Replacing the current surface parking lot at 1243 Olive Street, the new building will rise seven stories, containing 293 apartment units above 17,300 square feet of ground floor retail and restaurant space.  Phase two includes 7,000 square feet of residential amenities, with the added bonus of 24/7 on-site concierge and valet service.  Like seemingly every other low-rise development sprouting up in Downtown these days, the project was designed by TCA Architects.  Not coincidentally, 12th & Olive bears a strong resemblance to its phase one counterpart.  Owned by the Arizona-based Wolff Company, G12 arrives as the South Park neighborhood is on the cusp of a sea change.  Nearby on Pico Boulevard, Jade Enterprise's Onyx development is planned for two surface parking lots on the path of Metro's Blue and Expo Lines.  North on Grand Avenue, developer Mack Urban proposes multiple high-rise residential and hotel towers adjacent to the AT&T Center.