These are some examples of the ruins asset system my colleague and I used for our bachelor's thesis. We had about three months for the project, so our goal was to achieve as much variation as possible with a pretty small amount of assets. I modelled
my work at PI by alloa on Polycount Forum (Author's comment: You must keep in mind that for creating nice Stones/Rocks in this style the most important thing is the highlights. And in my opinion, all of your creation process depends on it.