Rooftop agriculture begins with the building. Confirm that the roof can safely support the proposed system, especially where wet growing media, water tanks or larger beds add load.
Plan drainage so that irrigation water does not damage the roof or create unsafe standing water. Access to a reliable water source and a controlled method of irrigation reduces daily labour.
Sun exposure and wind can be very different from ground level. Crop selection, shelter and support should reflect the actual rooftop microclimate.
Keep maintenance access around the growing area. A compact system is most useful when people can irrigate, inspect, harvest and clean it safely.