By using multi story buildings that are no longer being used by people or factories, hydroponics can be grown on the various floors. A source of light for growth is required. The best light is the sun, less costly and natural, however it needs to be distributed into the building. The light needs to sent into four floors covering a large area. To keep cost down no moving conveyors will be used. All plants will be stationary.

Theoretically or practically? Fibre optics carries light down fibres. So some form of thick fibre optic cable conveying light from the outside would do the trick. Or mirrors round the building - one set on each side set at 45 degrees to reflect light inwards into the floors. If you could rebuild then the use of glass building blocks would help.