Assembling a homemade refrigerator to achieve temperatures below -100°C is possible, but using liquid nitrogen (N2) is a common and effective method. Alternatives like cryocoolers, which consist of a compressor and cold head, can also be utilized, with types including Stirling, Gifford-McMahon, and Pulse Tube. The discussion emphasizes the importance of a vacuum jacketed container to minimize heat transfer when using cryocoolers. While liquid nitrogen is relatively inexpensive and accessible, dry ice can achieve temperatures around -79°C. The user's intent for creating such a refrigeration system remains unclear, raising questions about the purpose behind seeking extreme low temperatures.