I have a few questions, if you could please answer them:
How do you make your own models?
How do you make guns?
How do make money and a store?
How do you make a car?
Check out the posts in here that have tutorials and help on using Blender. That is the 3D modeling program to create that stuff. If you want shops and such check out the shop script in the tutorial section. Take care.
-mike