Truth is there are many programs out there which can let you create models.. most have pros/cons lists with them; for this game the list which can import are rather short unfort. It's basically Zmod2 or Blender which can import/export v3o. That being said, most any application which can dump to "primary" formats can with a little work be used for modeling. The only one I would suggest not even considering is sketchup, it does not convert well at all resulting in bloated un-optimized junk models. Aside from that most of the common mainstream apps, zmod1, zmod2, 3dsmax, blender all can be used with different processing to get the final product into the game. Sadly when people designed CAD software it apparently did not occur to them to standardize the things so that they are all using the same formatting for filetypes, axial alignment, automatic double-siding polygons etc... So those issues do come into play going from one program to another and must be corrected for should they present.
For now you probably do best to worry about finding a program and getting comfortable with it, I would not focus too much about figuring out how to get the end-result into the game (yet) till you've gotten it down on how to model the things, and are 100% sure you're into doing modeling before worrying about how to cross the bridge into importing them. Kind of makes no sense to build the bridge before you have traffic to travel over it in my opinion.
Goodluck.