The rock, of course -- You should have some notion of the kind you want, but I recommend that you not actually buy it until you have either a very good
idea of the scope of your project or the base of the wall already constructed. It's much easier to measure the base construction and then purchase the stone, so you don't have to sheepishly return to the rock yard and get six or seven additional square feet of material in order to finish the work -- not that I have eve
r had to do anything like that. Check with your stone supplier, but for stack stone
material you can expect to pay about $250 a ton with coverage of approximately 35 square feet per ton. For veneer stone
, you will pay approximately the same amount and get about double the square foot coverage. These prices reflect the stone available in the Atlanta, Georgia area and are not necessarily representative of your neck of the woods. The big determinants of the cost will be the freight from the quarry nearest you. Measure the project and add 10-12% extra; remember you will be chipping the rock away, so the waste is fairly significant. In any case, you will probably have to buy the rock by the pallet, so be prepared. Have it delivered; don't mess around hauling the stuff in 14 trips to your home. Don't forget to include the cap rock for the top of the wall.