This is a paid asset, but now you can download Top-Down Assets Free.
Detail this asset from Unity Store: Original Link
Top-Down Assets v1.2 (Latest version)
Beautiful and complete set to make a top-down view games: fantasy / rpg / hack ‘n’ slash.
Set includes about 90 models of environment: bushes, trees, trunks, modular ruins, modular buildings and lot of handmade hi-res textures (diffuse and normalmaps), 10 grounds, some particles etc.
This is exactly what you need for Your game