Ceiling

selectedSlot = 1

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

while true do
    while turtle.back() do
        items()
        turtle.place()
    end
    turtle.turnLeft()
end