This idea is so obvious that I’m flabbergasted the devs haven’t thought of it already. Basically, when you click on a building, if the advanced UI is enabled, we should see an icon for which resource (or resources) is being generated, along with the rate per minute. This would be updated according to civ bonuses, additional relics, etc. This was inspired by an Albanian concept I have where Castles generate a slow trickle of food and gold, but playing the Burgundian campaign reminded me of it.
Where this would be most helpful would be with the Feitoria. Players may not be able to tell how many resources it actually generates per minute.
If a building exchanges one resource in the stockpile for another, like say food for gold (as in the case of my Micronesian Stone Coin building), then the resource being subtracted from would have a negative value in the UI. In general, we need more transparency when it comes to buildings generating resources.