I made a grave error recently. I bought a lot of 2 X 4s to finish off my basement. Unfortunately, I couldn't get to it right away, and the lumber sat on the floor of my basement for about 5 weeks. Well, when I bought the wood, I selected each piece for straightness. Guess what? About 2/3s of them are all twisted and bent out of shape - useless except for starting a fire in my fireplace.
So, don't be like me. Buy your wood just prior to using it. If not, you may end up wasting a lot of money.