WallBuy Weapons

Im making a low poly fps shooter inspired by call of duty zombies mode, and i would like to add the wallbuy mechanic but have no idea where to start since i dont know much c#?

This one is fairly simple to do,

You can add a model of the weapon on the wall, add a collider over it.

Then you can do something like:

 void OnMouseOver(){
    if(Input.GetMouseDown(0)){
       // Remove some money, give player the weapon.
    }
 }

This will be the easiest bet.