What engine or technology are you using for your game; that is to say, what format do you need the map(s) to be in?

You don't need all the artwork to start development if you're planning on creating your own engine -- in fact, you're probably not ready for graphics until you've already put a simple triangle or square on screen and then moved on through displaying a basic cube and getting things working. If you're not sure about the format you need, you're not ready yet.


All that aside though, it sounds like you're probably not really ready to code your own engine either -- engine development is both difficult and time-consuming, and if you're not sure about what graphics-format you want to use or the basic logic of your game then it's highly unlikely you have the experience to tackle such a task. I would recommend using Unity3d, or some other existing engine to get some experience before trying to write your own engine.