You will need a large bread bowl, four 10- by 15- inch or larger baking sheets that will fit in pairs side-by-side in your oven, a sharp knife or razor blade, and a pastry brush.
Place water in a large bowl, sprinkle on yeast, then stir in 2 1/2 cups of the all purpose flour. Stir 100 times in the same direction (one minute) to develop the gluten, then leave this sponge covered with plastic wrap for 30 minutes or up to two hours.Stir in olive oil, salt, olives, and buckwheat flour. Mix in remaining flour, a cup at a time, stirring always in the same direction, until dough becomes too stiff to stir. Turn dough out onto a well floured working surface. Using floured hands, knead gently until the dough has an even consistency (apart from the olives), then knead 5 minutes longer. Clean bread bowl, oil it lightly, place dough in the bowl, then cover with plastic wrap. Let rise for 2 to 3 hours. It will have almost doubled in volume.
Oil two 10 by 15 inch (or larger) baking sheets. Flatten dough down gently with your hands, then turn out onto floured working surface. Cut dough in half, return half to the bread bowl and cover. Divide remaining half in two. Knead each half into a ball and then flatten gently with the palm of your hand. Let stand five minutes to rest. Working with each piece in turn, flatten out with your palms into a rectangle or oval about 10 inches long and 5 to 6 inches wide. It will be about 1/2 to 3/4 inch thick. Transfer each to a lightly oiled baking sheet at least 14 inches long. Let loaves rise for 20 to 30 minutes, covered with a damp towel or plastic wrap. Preheat oven to 400 degrees and set rack at the center of the oven or just above. (If your baking sheets do not fit side-by-side on one rack, place two racks in oven, one just above the center and one just below. One bread can go on each rack; about halfway through baking (after 10 to 12 minutes), switch the two around.) Just before placing in the oven, use a sharp knife or razor blade to make cuts through the breads: Starting two inches from the top and about an inch from the side, cut across the bread to within an inch of the other side. Make two more cuts, parallel to the first, at about 2 inch intervals (the cuts should go all the way through the dough). The dough will separate at each cut, so that the bread looks like a kind of fat-runged ladder; you can pull dough apart even more if you wish and if your baking sheets are long enough, by pulling gently on each end of the breads to make the slits gape more. Brush each loaf lightly with olive oil all over, place in the oven, and bake for 20 minutes. Breads will be golden when done.
Once first two loaves are in the oven, oil two more baking sheets, then flatten remaining dough, divide into two, and repeat steps required to form loaves. Breads should almost have finished rising by the time the first batch comes out of the oven.