I've made a topdown shooter based on your graphics. It's still in it's early versions so some animations are not complete and towers and some guns have not yet been implemented. It's for iOS devices and works with both iPhone and iPad.
I've used the colour palette to create some more graphics, and I've made a new map and changes a few of the game mechanics from the gif.
PS. I'm just starting out at coding and am new at Xcode. I'm only 12 so don't be too harsh.