A rooftop garden structure was installed on top of a 20-foot freight container plant factory in MARDI Serdang, Selangor. The rooftop garden consists of three major components: a rain shelter, a reticulated hydroponic growing system via Nutrient Film Technique (NFT), and a chiller system to chill and control the nutrient-water temperature in the fertiliser tank. Lactuca sativa was cultivated using root zone cooling, with a hydroponic setup at ambient temperature as a control to study the root zone cooling system (RZC) on the crop yields in the tropics. The weight of crop, root, leaf width and leaf numbers of Lactuca sativa have been selected as yield parameters, recorded, and analysed. From the results, all the growing parameters performance for Lactuca sativa grown in the root zone cooling method were found to be better than control. For yield parameters performance, Lactuca sativa grown in control was better than the root zone cooling method. The yield weight for Lactuca sativa cultivated as control is higher than the RZC system by 39.4%, ranging from 36.69(39.04 g as control) and 20.59(23.66 g) RZC method. Roots weight for Lactuca sativa cultivated as a control method is better than RZC by 14.1%, ranging from 5.73−6.22 g using control) and 4.69−5.34 g by using RZC, respectively. The number of leaves for Lactuca sativa cultivated as a control method is more than RZC by 26%, ranging from 14−15 as control and static at 11 using the RZC system. The leaves dimension for Lactuca sativa cultivated as control is more significant than RZC by 48%. The Lactuca sativa leaves dimension cultivated as a control method is from 580.35(670.27 cm2, while RZC is from 318.68−348.45 cm2.