dont make it it web based and dont based of on lin-city(NG) eather you shold base it on Open city if you really want somthing good and it shold be a downloadable client and it shold be for Windows, linux and mac
OpenCity is a full 3D city simulator game project. It is written in standard C++ with OpenGL and SDL from scratch. It is not intended to be a clone of any famous city simulator from Max*s. So, if you are looking to download a free SimCity 4 like, please forget OpenCity. At the meaning time, you can build roads, electric lines, electric plant, trees and the three standard RCI zones.
http://www.opencity.info/
http://sourceforge.net/projects/opencity/