Rain Garden

As part of the drainage plan, there’s a ‘Rain Garden’ feature that is supposed to help with the water as it runs off the house.  This Rain Garden will be beyond the deck in the back and I guess the runoff from the roof will go there.  In the property behind us is a drain with a culvert that runs under our property (behind the old building), under the road and exits someplace after that.  The builder is mentioning a cost of $5-6K to build this.  Yikes.