That's a great start! Will you be adding any washes or using artist's oils for added color depth?
A simple black wash from a drop of enamel and an ounce of mineral spirits will bring out all the 3D detail. A soft dry brush with a light colored artist, tube oil, like a yellow ocher will highlight the sun bleached spots.
Painting stone walls is a lot of work. But the results are well worth the time.
Here's a similar type building in 1/35 which is nearly done now. It's made from MDF and covered in polymer baking clay.
http://www.modelarmour.com/index.php?option=com_jfusion&Itemid=81&jfile=viewtopic.php&f=13&t=7779&start=10