There are a large number of precast frame buildings used in Turkey for industrial facilities. One-story warehouses are the most common structural configurations. Because there was little redundancy in the lateral load resisting system, many precast buildings were damaged beyond repair during the 1999 earthquakes in Turkey. In the present study, a rehabilitation scheme is proposed to add a structural diaphragm at the roof level by adding diagonal bracing. With the diaphragm action developed, the lateral forces can be transmitted among the cantilever columns, and to the vertical diagonal braces on the periphery, thus the seismic performance can be enhanced. An analysis method is also developed for the rehabilitation design.