Actually, I could share it here I guess.
In my game the player will be protecting Earth again a alien invasion. A missile will be built at the background to destroy the mothership. The player will have a few weapons to shoot the incoming waves of different enemy ships, scrap metal will be dropped by the ships and by selling it the player will get currency to upgrade the weapons or hire more engineers to build the missile faster.
That's the main idea I guess. Don't mind the quick sketch I made on my phone, it should give you a clearer picture tho . it's a real bad drawing haha