The California Department of Transportation has signed the last of four agreements authorizing the development of privately financed toll roads. The agreement with a consortium headed by Texas computer magnate H. Ross Perot permits construction of a $700-million, 11.2-mile toll-road extension of California 57 in Orange County. The four-lane tollway will link Interstate 5 near Anaheim Stadium with Interstate 405 near John Wayne-Orange County Airport. The toll-road projects were approved by the Legislature last year, but it was left up to Caltrans to determine which projects would be built and which private group would build them. Once completed, the roads will be deeded to the state and then leased back to their developers, who can make a profit by charging tolls for the next 35 years. The amount of the tolls will have to be approved by the state.