CobbleCeiling

selectedSlot = 1
possibleBack = true

function items()
    if turtle.getItemCount(selectedSlot) <= 1 then
        selectedSlot = selectedSlot + 1
        if selectedSlot == 17 then
          selectedSlot = 1
        end
        turtle.select(selectedSlot)
    end
end

turtle.select(selectedSlot)
while true do
  possibleBack = true
  while turtle.back() do
    possibleBack = false
    items()
    turtle.place()
  end
  if possibleBack then
    turtle.down()
    turtle.placeUp()
    while turtle.forward() do end
    turtle.turnRight()
    while turtle.forward() do end
    turtle.turnLeft()
  else
    turtle.turnRight()
  end
end