I always check the boards at HD or Loews before buying them. Make sure the lumber is completely dry to the touch. I use the concrete floor as a level and check all sides. I may go through many, many boards to select what i need. Just dont compromise. If they ask me what I'm doing I tell them or show them.
Then, it's best to use them fairly soon and do not let them get hot or in the sunlight. Treated lumber and cedar are the worst for twist/curve.
I think the attic of my house was made from specially selected wood like you have. I just figure Salvador Dali was on the crew that day and shrug it off.
