I would be great if you could create a free roam map like island Panau in the game Just Cause 2, by Eidos Entertainment and which uses the Avalanche 2 engine. It has four regions; desser, Snow mountain range, forest(different types) and city. It really interesting like Crysis and Gta 4 smack together, good game too.
Take a look here:
I think the fans would like this, Motorm4x is free roam too, but maps are far smaller