An idea could be to put the upgrade % and time remaining in the "upgrade button" so you can see that the building you have clicked is being upgraded. When selecting building via ressource window when trying to upgrade several buildings, you do .. OK I do, miss that I select a building already upgrading, and tend to click the upgrade button several times before finding out that it is already upgrading. (there is actually no indication at all that you're updating a building, when it is selected, and I find that ... annoying)
Good idea...
Ahileus @ The Immortals [IMO]