Some buildings are related and it is possible to upgrade from a one version to the other, by paying the difference PLUS one BP per size of the new building, assuming there is space available for the extra development. This means you can start small and build up later :}
These are the most obvious chains – However, you may try and negotiate others …
Barracks
Watchtower
Garrison
Castle
Ale House
Tavern
Inn
Hut/Tenement
House
Mansion
Noble Villa
Shrine
Temple
Cathedral
Quay
Piers
Waterfront