Fill in cavities on a rock where a cottage is to stand. How do you do it?

[Återfall]

Building a cabin on a mountain, and wondering what to do about larger holes/indentations in the rock?
I don't want to risk water standing under the cabin. What should I do, can I fill the indentations, and if so, with what?

Thanks!//Anders

Here's how it might look. In one of the pictures, I've filled the "hole" with larger stones. The hole is about 30 cm deep:

 

[GoForIt]

A little concrete?