A group of investors hopes to convert the 3.5-million-square-foot Packard Plant in Detroit into a mixed-use development costing an estimated $350 million. Precast concrete walls would be used for residences and some of the former auto plant itself. Albert Kahn Associates -- which designed the original complex -- will serve as the project's designer. "The bones are still good," says Rick Dye, a principal at Albert Kahn. "If you look deeper ... it looks like the concrete is holding up pretty good. There are still decent structural capabilities."