To prevent abuse and make things more realistic, the structures that you build only appear when you have used all your building turns. I.e. if it takes you 30 turns to build 10k smithies, they won't produce any troops until AFTER you've finished the build. Until now, the game acted like all 10k smithies were instantly available, and producing troops for those 30 turns.
The same applies for demolishing, i.e. structures are active while the demolishing is being done. This is less realistic but does prevent abuse.
Incremental building would have been nicer, but much harder.