Just a thought. Having buildings built on a rating system.
It could be on a 1 to 5 star rating where the building would become more effective but cost more hammers based on the scale. Say you were building a barracks in a city, the higher rating you commisioned the building, the more xp it grants to a new unit. If you build a level 1 building, later on you would could have the chance to upgrade it but it would cost more hammers. This would be could if you were going for speed and just need a little boost or if you were trying to create mini wonders of the world. It would give cities a little more distinction such as the Great Colosseum of Rome.
It could be on a 1 to 5 star rating where the building would become more effective but cost more hammers based on the scale. Say you were building a barracks in a city, the higher rating you commisioned the building, the more xp it grants to a new unit. If you build a level 1 building, later on you would could have the chance to upgrade it but it would cost more hammers. This would be could if you were going for speed and just need a little boost or if you were trying to create mini wonders of the world. It would give cities a little more distinction such as the Great Colosseum of Rome.