Trying to create a game inspiring by worldbox (god simulator)

So, I had an idea in my mind for a long time now that I would like to discuss with you all. I love games where it runs itself... like worldbox... if you haven't played worldbox yet, you can download it on your iphone/android from the app store.

Worldbox is where you get to create a world the way you want (mostly the game is pixel based). You can design the world using physical features the way you would like to look. You can put the first man/human on the map and watch them survive/reproduce to make more humans eventually building things of their own like houses, farms, roads, cutting trees, mining gold, etc. Eventually, they create and expand their territories, building villages and eventually their own empire. The game engine also includes wars as well.

What I am trying to do is build something similar in function but a little different but I am confused as to where to start from. What resources do I need? There are many different game building software out there. I am looking for something that is easy to use software, free if possible. Any suggestions?