How close can you build next to leyandii of about 25ft?

When building next to Leylandii trees that are around 25 feet tall, it's generally recommended to maintain a distance of at least 2 to 3 meters (approximately 6 to 10 feet) from the base of the trees. This distance helps to minimize potential issues with root intrusion, shading, and falling branches. However, local regulations and specific site conditions may also influence this distance, so it's advisable to consult local planning guidelines or a professional before proceeding.