My friend did a DIY for his rain water harvesting solution, but it was all done at his backyard. Basically he asked the contractor to divert the water from the roof into 2 large 100 gallon tank at the back. The tank he converted it by adding a pipe between the two tanks so that it shares the water and it becomes 200 gallons in total and an external pipe. Mainly uses the water to either water the plants behind and clean the back porch area. He has a large space at the back of the house, almost 20 feet.