Start by crisping up the corn tortillas (if using ready-made tostada shells, you can skip this step). Heat the oil in a skillet over medium-high heat. There should be enough to form a thin layer on the bottom of the pan, so use more if necessary. Add tortillas one at a time, press down with a spatula, and cook for about 30 seconds to 1 minute per side. Set on a wire rack, where they'll crisp up as they cool.
Preheat broiler (mine doesn't have variable heat settings; if yours does, choose a medium setting). Set tostada shells on foil-lined baking sheets (you'll probably need to do two batches).
Mix the chicken with the buffalo sauce. If needed, season with salt and pepper.
Divide chicken mixture evenly among tostada shells and top with shredded cheese.
Broil for about 2 minutes, just until cheese has melted. Broilers do vary, so I suggest you check a little earlier to make sure the cheese doesn't burn.
Top with as many of the other ingredients as you like (I prefer to dollop on some sour cream first as it helps the other toppings stick). I have listed what I like to use, but I'm sure there are all kinds of things you could add.