Hi, sometimes I charge hourly, but I'm trying to charge by the square foot more, its so much easier bundling up all the materials and labor.. I use alot of quarried stone, fieldstone, etc.. As for retaining walls, do I calculate in the top of the wall? L X W for the face of the wall, but the capstones, should I measure the top surface of the wall, say its a foot in width by 40 ft long.. would you add that to the total sq. ft. of the wall's face? It takes time and much effort to get that nice flat top, using irregular stone. Thanks for any tips!