The use of olfactometers to study rodent behavior and brain activity during olfactory tasks is crucial for understanding brain circuits. These sophisticated devices allow researchers to precisely control and deliver odor stimuli, enabling the investigation of complex olfactory processes in rodents. Although commercially available olfactometers are convenient, they present challenges when technical issues arise, often requiring costly assistance and potentially disrupting research timelines. This article details the construction of a custom olfactometer specifically designed for mouse olfactory behavior experiments, providing a comprehensive list of parts and step-by-step instructions. The olfactometer is controlled through MATLAB, offering a user-friendly interface for researchers. Importantly, the open-source code allows users to modify and adapt the system, tailoring behavioral tasks to meet specific experimental needs. Building a customized olfactometer empowers users with the knowledge and capability to perform custom experimental design and troubleshooting independently, saving both time and resources. This approach not only enhances research flexibility but also fosters a deeper understanding of the equipment's functionality, ultimately leading to more robust and reliable olfactory studies in rodents.