My neighbour designed his own system using coiled pipe.

You would get 3 times more heat from a single 4x8 collector (approx. $280).

If black polypipe, coiled onto your roof, offered adequate heat, professional solar, gas, electric and oil heating systems would be obsolete. A homemade solar system, comprising of 1000 feet of 1.5 inch black polypipe at $0.69/foot offers about the same amount of heat as an 8'x4' polypropylene collector at $280! You will need about 8000 to 10 000 feet of coil to heat your average pool. Unfortunately, it won't fit on your roof, won't drain properly if it is coiled, will require hundreds of roof perforations, is terribly unsightly, and it will overload your pump.