Here is one I have done for my
WIP Custodes. It is quite close in, but it gives you a good idea of the effect I was going for, which is the deepest darkest basement of old Terra. Deep in the Imperial dungeon where the most dangerous creatures are held, the floor is old rough stone paced by grim faced wardens.
It was fairly easy to achieve. Milliput rolled out and put on the base, a decent sized stone was pushed gently in to get the rough imprints then the tiles themselves were just marked out with a sharp modelling knife. Paint/wash and drybrush to your chosen colour.
Things to bear in mind, the more you push the stone in, the rougher the surface. If you want to keep it pretty smooth you can be very gentle to get a very light effect.