Also if you need help to build your city, look at this checklist (it might not be complete but it'll help) : 

-Why is the city built where it is? 
In europe during the Middle Ages, people often built their cities according to 3 factors :1) Water/food access (rivers were largely preferred due to the abundance of both, and also allowed trading), 2) Militarily easy to defend? The town I come from is in the loop of a river and on top of a hill, so if a bunch of soldiers came running at it, they'd likely be dead by the time they reach the city gates since there's only one way to get there. 3) Trading is facilitated there/locals are nice and we want to trade with them. Big cities are often situated along some sort of water site which allows them to get heavy and valuable things to other cities way more easily. The best cities were a mixture of all of them. 

-When was it built? This determines the presence of old neighborhoods and whether they could be used as a way to attract tourists. But old cities also says less tolerant inhabitants and more rampant racism. (See : Europe once again). Also, old cities have more small and sinuous roads, whereas new cities tend to be quite squared. (For example, compare Bordeaux to Abu Dhabi.)

-What attracts people there? Is it jobs created by a particularly large industry (Like Detroit and its cars)? In that case, much of the old city will be situated around that industry. Or is it like Las Vegas or Los Angeles? Anyhow, you need to determine the prime industry of your city and how people would try to live around it.

- What keeps people there? Is it a good quality of life? Is it the attractions around the city? Etc, etc. 

-Is it important enough to have an airport? In that case, a large part of the city would be dedicated to trading and storing the goods- a lot of warehouses would be around the airport (Same with a port)

-RELIGION. What is your city's first religion? Is it  christian? Then a lot of churches and cathedrals would be around the city. If there are ten million people there, there would also be a ton of different other cults so mosques and synagogues would be there, but less prominently than churches. 

-Industry. Is there a large manufacture sector? Does your city import or export more? What does it import/export? Or does it only import? There's bound to be an industrial sector anyways, but how big would it be?

-Business. Would it be attractive to companies? How so? Is there any natural resources/legislation that would draw the companies to build things there? Would some of them have their headquarters built in the city? 




I'm sorry if this is a lot, but I am particularly fond of history and those are most of the factors that people can find in most nowadays cities. Feel free to message me if you need any help :D