So two people (myself and Nimesha) working for about four months straight, I think. Mostly eight to ten hour days. Three academics helping us find data for when public sources ran dry (especially flow along the corridors) - see the workflow at https://github.com/team-watchdog/colombo-skylines/wiki/Intro...

You can download a height map file from https://terrain.party/ or https://heightmap.skydark.pl/ and start a new game with the unlimited money cheat. Then it's just a matter of placing roads, utilities, public services and zoning the rest (that's the fun part).