The western approach would almost certainly be a public-private partnership; we do that with all meaningful infra projects, where multiple industry consortia put together proposals and then one is selected to move forward. For example, for the ION Light Rail in Waterloo Region (~$1B), the winning consortium was composed of engineering and construction firms/consultants, a operations company that would run the system, plus a financier: https://en.wikipedia.org/wiki/GrandLinq

That said, for a project the scale of building a city, I can imagine it might actually be faster and more efficient for the government to just plan and build everything itself and then sell it off to private entities later.