Fernando Robert Yu
I was playing with a group of friends and one of them built her first stage of side B within the first three turns, when there was no discard pile.
We were at a loss for what to do since she had no discard pile to pull anything from. In this case, we let her take something when the age ended, but for future instances, what's the proper course of action?
She gets to build nothing, since there is no discard pile. It is best to wait to build the wonder stages of this city in the middle to late game, and it is a good idea to discard a few cards which you and your opponents want, but would cost you too much (or you are unable to) build.