I enjoyed this game!
I didn't notice you could upgrade multiple times at first and was about to get carpal tunnel from all the clicking but after a while I noticed I could keep upgrading and get lots of materials at a time. XD
Nice 3d models and fun game. The sounds were great too!
I placed a building a bit too close to the mine and it became a bottleneck for the little workers, but apart from that I don't think I found any game breaking bug.
Nice work!