Thanks everyone for your engagement on this.
Concerning the logic of autogen having a binary switch between always barns or always apartment blocks - I was hoping a (hopefully) simple algorithm mod to decide on each based on:
i) its surrounding building density (say, within 2km - might need some experimenting with settings).
A high density of surrounding buildings indicates an urban setting, i.e. place an apartment block, but a low density causes the placement of a barn.
OR
ii) Maybe a specific definition of urban land areas would help autogen select the appropriate building class for urban and rural (rural includes villages) - not just barns/apartment blocks.