Stairway

print("To Heaven!")
args = {...}
length=tonumber(args[1])
slotNum = 1
function checkSlot()
  if turtle.getItemCount(slotNum)==0 then
    while turtle.getItemCount(slotNum)==0 do
      slotNum=slotNum+1
      if slotNum==17 then
        slotNum=2
        turtle.select(slotNum)
        print("Add more material.")
        while turtle.getItemCount(slotNum)==0 do
          os.queueEvent("randomEvent")
          os.pullEvent()
        end
        print("Ok. Continue.")
      else
        turtle.select(slotNum)
      end
    end
  end
end

function place()
  checkSlot()
  turtle.placeDown()
end

for i=1,length,1 do
  turtle.up()
  place()
  turtle.forward()
  place()
  turtle.forward()
end