Building Randomization
Building plans are selected at random by your settlers within the pool of available buildings for the plot type you created.
This is done for two reasons: 1) The game engine does not support a dynamic menu system, so direct choice would require someone manually managing every single add-on packs building names - which would take away from the dynamic nature of the addon system, not to mention, after a few more months, we'll likely have hundreds of building options which would not be good for gameplay. 2) The idea behind Sim Settlements is that you're now just worrying about the macro level of Settlement building, while your settlers live their lives within the basic framework you lay out for them.
There are a few exceptions to the randomization:
Commercial - Commercial properties will first ensure you have one shop from each category before completely randomizing.
New Building Priority - Sim Settlements will prioritize building plans you've never seen before. So if you install a new add-on pack, you can be confident it's models will be more likely to come up once each before they are shuffled in to the random pool.
VIP Homes - The VIP system only works on certain models, due to how complex the props are, they are designed around those models. So if a settler is randomly given a VIP story, they may choose a specific model house, even if New Buildings models are available you haven't seen yet.
Future of Randomization - In the future, options to ban specific models, and to choose an overall theme for a settlement will be implemented to help give you more control over which building plans are used.
