animating, physics, and damage points... ((animating))

My question is about the subject and I am creating a game here in Unity using terrain as the floor so its outside you know and it is first person also. The point of the game is see how long you can escape the apocalyptic fire balls falling from the skies and to dodge them I will be making my own dodge commands like left dodge and so on but you can control the view with the mouse so you see the freedom i have here.
My question is I wanna know how to start when it comes to the animation of the boulders that'll be falling from the skies and this question is simple it is i just wanna make them roll to the like for say y axis while I had it set on a rigid body ( ican figure out how to spawn multiple ones and in random places) i just dont know how to animate the moving boulders falling from the sky any idea on a couple steps to start me or atleast a page with the animations window of commands and excercises etc... Appreciate your time to help me lots i really really do :]
-Johnny Rocket Fingers