Memories; past experience; aspects of self put in storage, such as ambition while bringing up children.
In many films warehouses are often used to show criminal or murderous scenes. But in peoples dreams they can be about any activity. So look up the activity for clues to its meaning. See What is the main action in the dream?
Example: I took LSD given me by Ann. All sorts of things happened. I was going up in a lift, and a very beautiful girl got in. It then seemed as if we went into another dimension. Possibly she had tricked me into having sex with her. Anyway, we walked into a huge warehouse place, and there were glass cases with us at various stages of the future. In one case, we had three daughters, very lovely. Then, as we progressed into time, it was as if body changes took place, and the fingers became segmented, and the face changed. Then we were back in the lift. There were various other experiences, and then I was back in the house, coming out of the LSD. All the colours were very bright still, I began to tidy up the furniture, and realised it was morning and I was not tired from a night of being awake.