This app was mentioned in 3 comments, with an average of 2.00 upvotes
Sounds like a great idea, but you'd definitely have to get your applications process sorted. If you become popular you'd probably be inundated with requests.
Speaking of which... would be great if you could check out my strategy game https://play.google.com/store/apps/details?id=com.boondog.games.android
The gameplay is exactly what you describe, and it's free and ad-free:
Dinowar https://play.google.com/store/apps/details?id=com.boondog.games.android
Full disclosure: me and a friend wrote this
Dinowar, offline you don't get the achievements but can still play the full game