Many buildings have complementary relationships with each other.
A Forge and a Blacksmith here have different functions, but one needs the output of the other to produce their product.
Having the artwork of the two different buildings complement and integrate into each other when placed next to one another, might be cool.
Similarly, the Barracks building could be designed in such a fashion that when two, or even four are placed together, it would look like one large fortress, rather than a bunch of smaller buildings in a group.
With such an already beautifully designed game, this would be a great addition, vines growing up the sides over time or ivy, certain buildings changing architecture if they’re built next to another one and kind of becoming one larger structure.
Aren’t you perhaps really after more modular buildings? So instead of juts plopping down a “Foundry”, you could assemble a one out its various subcomponents, and likewise a Blacksmith Forge; when you have all of them you get the fully functioning asset, but still get partial functionality with a sub component. If you look at the Foundry model you actually have 3 subcomponents that all could be arranged in different ways and each provide a different function - there is the main building, and a couple of side buildings for storing inputs and outputs - and notice how all 3 of these things are also in-game functions. You the player could lay them out in one o several different configurations: the models are all already there in game, so this shouldn’t be difficult to do. (ou could keep the current configuration its a default on, and have a button to click if if you want to change it, if you don’t want the default gameplay experience to be any more complicated.)
And when you come to place you Blacksmith Forge, you could arrange its sub-sonnets in the way you want to - and thereby in a way that suits how you made your foundry.