Bought a house five years ago with about a 500 square foot covered patio roof. The roof consists of 2x6 timber rafters supporting 3/8 inch 8x4 foot plywood sheet underlayment, roofing felt and asphalt shingles. The problem is the plywood has buckled mainly along the joints creating numerous leaks. Time to replace the roof. First question is what went wrong? Second, how do I prevent that from happening again? Third, should I consider using other materials besides what is there? A few things to consider. I live in a desert region. We get moderate rain from Jan through April and little thereafter. Summer temps reach a consistent 95 to 105 degrees. There is no covering on the bottom of the roof. I can stand on the patio and see the bottom side of the plywood underlayment. I appreciate any suggestions.