This is a great project for G+T students in fifth and sixth grade. Variations I have done include working individually and letting the students choose anywhere in the world they would like their country to be. The geography and climate of their portion of the earth affects the other aspects, such as history, customs, foods, etc.
This group project has students creatively create a country from scratch while incorporating academic information learned during the year. There are 15 items the students must address to varying degrees of depth (all detailed in the handout).