The trouble with the "add" number being bigger is that you want to keep overall building count down, to reduce server load.
If someone can make a city more efficient by building 100 tiny arenas rather than 1 big one, they will.
It also makes little sense. Making one multiplex cinema should be more efficient, somehow, than building five different cinemas. Trouble is, in real life you can't just build an "office" of so many metres cubed. If you build one, you also need to connect the pipes, build the foundations, fire escapes etc. Adding a second office to that plan is relatively trivial. Effective pop limits are reasonably low now, as it is. Removing the "add" penalty will probably limit the number of buildings in most cities by a good few dozen.
You could even have a penalty for the first office instead, to represent all the infrastructure needed to build the edifice, then a reducing cost as you add more (up to a point), to represent the relative ease of extending that infrastructure between floors, wings, etc. There's a reason why people build extensions rather than just building a new house in the garden!
If someone can make a city more efficient by building 100 tiny arenas rather than 1 big one, they will.
It also makes little sense. Making one multiplex cinema should be more efficient, somehow, than building five different cinemas. Trouble is, in real life you can't just build an "office" of so many metres cubed. If you build one, you also need to connect the pipes, build the foundations, fire escapes etc. Adding a second office to that plan is relatively trivial. Effective pop limits are reasonably low now, as it is. Removing the "add" penalty will probably limit the number of buildings in most cities by a good few dozen.
You could even have a penalty for the first office instead, to represent all the infrastructure needed to build the edifice, then a reducing cost as you add more (up to a point), to represent the relative ease of extending that infrastructure between floors, wings, etc. There's a reason why people build extensions rather than just building a new house in the garden!