Do you have any experience in writing games at all? Are you familiar with the algorithms and mathematics required to program such a thing? And if you are going to use Unity, are you familiar with C#/Javascript? I would recommend looking into these things before you begin.
Here is a good 3d math primer if you are a motivated person. It is very easy to understand and should teach you enough to begin your journey into game programming if you haven't already done so. Don't expect for this to be a success if it is your first game, but whatever it turns out to be you will surely gain experience from it. Good luck!