Reptile Forums UK - This recently updated thread shows some great step-by-step instructions for building a rock background out of foam, grout, and paint.
Mayan Themed Rock Background
May 9, 2012
by Asst. Editor in Chief
Geckos Unlimited - Get start to finish photos and information about a very nice Mayan/Incan themed fake rock background that a member built for use in an Exo Terra terrarium.@ Geckos Unlimited