Hi Wraith, welcome to the Guild.
If you are interested in making a 3d model of a city, be aware before you begin of what you are getting yourself into. My city of Birdseye was not originally meant to be a 3D city, but I have now begun modelling it (with help from another member of the Guild), and so can offer some advice (there's a link to the WIP in my signature).
I use SketchUp, which has the benefit of being easy to learn and use, and being free. The disadvantages are that it is not very good at handling textures/materials, it can get complicated if you want to export files to another modelling software, it often doesn't look great unless you have a more advanced kind of rendering software (which again raises the problem of exporting files), it is difficult to make terrain or organic-shaped objects, and it can get very slow if your city is large and detailed.
I'm not so familiar with other 3d modelling software. I know that Blender exists and is free, but has a steep learning curve (you get what you pay for). 3D Studio Max is an expensive option but I think it is reasonably powerful, although again, it helps to have a little background in modelling programs (which I don't have).
Overall, ask yourself why you want to make a 3d model (how will it be used, why make it in 3d and not just try to draw it etc), how much time you have to give to the project, and what level of expertise you have in 3d modelling.
Having said that, I can confirm that trying to make a whole city is exhausting but extremely rewarding, and the results can be absolutely stunning (if I do say so myself).
Good luck with it. And maybe you should post some work in progress pics here on the Guild.