Donald Thomson’s water bottle solution? Throw them on the roof. Donald Thomson, a 56-year-old, Canadian-born builder, entrepreneur and self-taught designer, launched ‘A’Gua-brand water bottles in Costa Rica earlier this year. But he sees no contradiction in his current endeavor: converting reclaimed, custom-designed, PET plastic water bottles into roofing tiles that are filled with an insulating, lightweight mix of aerated concrete and waste paper, which can be tinted to simulate marble, slate or ceramic tile. (He…