I am interested in have an earth sheltered home designed and engineered by professionals. I need to know more about the cost of prestressed concrete planks as a roof before I request, or require their inclusion in the design. I do not know if a (for example, 4 ft x 32 ft x 8 inch) plank will cost $200 or $200,000. I have no clue. Any help or experience is appreciated.

Contact a local supplier for rough pricing. You can find them thru PCI (Prestress Concrete Institute) in Chicago. Most reputable suppliers will be members.

Also, your design professionals should be able to guide you on what systems are most cost efficient for your project.

Your biggest concern will be how you handle waterproofing. It could make or break your project in the long run.