Create terrain with grid

Hi guys!

I'm developing a RTS game and I cannot simply find a good tutorial or script that does what I want/works. Basically, I need a script which would project a grid on my terrain, and if I mouseover a grid "cube" it should highlight, to make it easier to place objects later on. How would I create this grid in unity, project it on my terrain and highlight it when mouse is over (probably something with raycast here...)? I would appreciate logic or scripts, I really need this to my "kind of RTS" game...

Thanks!