Stone Base and French Drain Telford PA After the french drain installation is complete, final grading of the site makes sure the dirt surrounding the pole barn is level and secure. A french drain system is added to reduce the amount of sitting water around the barn by redirecting it elsewhere. After the pole barn is built, stone is added to ensure the base of the barn stays level and secure. The shed is removed, and excavation of the site in preparation of the pole barn is almost complete! Before construction starts, the shed needs to be removed and the site needs to be leveled.