I find it pretty inconvenient, to check if a building has been upgraded.
We must klick on it, then tabs, then; ah ok, all upgrades are checked and active.

Suggestion:
- a logo / icon over the builing in the city with no-upgrades / x on y upgrades / full upgraded
- Or, improvement on the building with more parts: a plant could have some more accessories on its landsquare or on the roof, so we can see that it's a 1-cannery/2-partially improved cannery/3-full upgraded cannery