Neater is Better

What did I do?

• Finally, I solved the problem of tower placement. Instead of using Camera.main.ScreenToWorldPoint(Input.mousePosition), I used Physics.Raycast to find the coordinates to build tower.
• I added health bar over enemies. But it's position is not consistent (Because of different resolutions). I will fix that problem.
• I deleted the ellipse-like shape under the tower to detect enemies. I used Physics.OverlapSphere, instead.
• I added enemy spawner.
• I created a transparent clynder and made y scale value very low. Thus, I obtained a circle. I used it to specify the fire range of the tower.

You can play this version of the game here.