you are making a realistic(preferably) , open world, city based, top down shooter game. your character is able to buy weapons', take cars, buy houses, change clothes, and lots more, this can be freeplay or story based (that's your choice). if its freeplay make sure that you can customize your own character. for movement its w to move forward and mouse to move the direction your character is looking. make a police function so you can be shot down  and die, if you die a 5000 dollar hospital bill is directly paid from your account if you don't have 5000 you will just lose as much as you can. this can not be too realistic as it needs to be able to run on a light pc for maximum playability, if you want to make it multiplayer you can. you have one month to finish good luck.