Get the "Random Tools" extension either from here or using Extension Warehouse in Sketchup.
I did this flat on the ground or a top view.
Create a hexagon pattern like this.

Select all and click the second icon (Random Vertex Positions) in the Random Tools menu.

Apply something like the following setting. You may have to play with it depending on the size and units of your model.

Results.

You should be able to take it from there by adding random texture positions, border elements, etc.

















