Every time I've bought treated timber, they are straight from the lumber yard but after a few days they look like a roller coaster. If I am going to build something with a lot of timber as beams, floor joists, etc., they will be sitting for a while before everything is in place. How should I store them to avoid warping? The forces are quite substantial, so a beam resting on slabs instead of being anchored in posts might surely lift off the ground.
The sun is your biggest enemy in this situation, stack properly, use tension straps if necessary, and cover against sunlight.