If this game isn’t “expansion” then I don’t know what is! City building was a great choice. I think your game would benefit greatly from a few minor adjustments. The most crucial, imo would be to show the player where exactly the selected building is going and what it’s dimensions are. At the moment it takes a bit of guesswork or trial and error to understand building placement.
This next bit is probably just because i’m an audio guy. But some simple SFX and background track would make this a much more pleasurable experience.
I hope you work on this further as there is definitely potential for a solid game here.