City building game upgrade system

Hi I am new to unity answers and just wandering how to code a city building game upgrade system.
The script should pop up a UI asking if you want to upgrade it and if so , a timer will start. When thats done just replace with something else.
I would be glad if someone could help me with that.

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Thanks for your quick answer !
As you may saw in the photo am I a beginner to Unity. I am trying to make a upgrade system for games like “Clash Of Clans” or “Lords Mobile”. I really this is enough for you to help me !
And again, Thanks for the answer came so fast !

theyre not going to answer you i hope you know this these systems are useless