Minecraft Turtle Auto build column v1.03

tArgs = {...}

local currentLevel = 0
local build = false
local currentSlot = 1
local size = 1

function isEmpty(slot)
  if turtle.getItemCount(slot) > 0 then
    return false
  else
    return true
  end
end

function nextSlot()
  currentSlot = currentSlot + 1
  turtle.select(currentSlot)
end

function buildColumn()
  while turtle.detectDown() == false do
    turtle.down()
    currentLevel = currentLevel + 1
  end

  if turtle.detectDown() == true then
    for i = 1, currentLevel do
      if isEmpty(currentSlot) == false then
        turtle.up()
        turtle.placeDown()
      else
        nextSlot()
        turtle.up()
        turtle.placeDown()
      end
    end
  end
  currentLevel = 0
end

function buildTwoByTwo()
   buildColumn()
   turtle.forward()
   buildColumn()
   turtle.turnLeft()
   turtle.forward()
   buildColumn()
   turtle.turnLeft()
   turtle.forward()
   buildColumn()
   turtle.turnLeft()
   turtle.forward()
   print("DONE")
end

function buildThreeByThree()
  buildColumn()
  turtle.forward()
  buildColumn()
  turtle.forward()
  buildColumn()
  turtle.turnLeft()
  turtle.forward()
  buildColumn()
  turtle.turnLeft()
  turtle.forward()
  buildColumn()
  turtle.forward()
  buildColumn()
  turtle.turnRight()
  turtle.forward()
  buildColumn()
  turtle.turnRight()
  turtle.forward()
  buildColumn()
  turtle.forward()
  buildColumn()
  turtle.turnRight()
  turtle.turnRight()
  turtle.forward()
  turtle.forward()
  turtle.forward()
  print("DONE")
end

if tArgs[1] == nil then
  print("Building a 1 x 1 column")
  build = true
else
  if tArgs[1 == "2" or tArgs[1] == "3" then
    build = true
    size = tonumber(tArgs[1])
  else
    print("Invalid Usage.")
    print("Usage:")
    print("column")
    print("column size")
    print(" ")
    print("Valid column sizes: (2) = 2 x 2, (3) = 3 x 3, (4) = 4 x 4")
  end
end

if build == true then
  if size == 1 then
    buildColumn()
    print("DONE")
  elseif size == 2 then
    buildTwoByTwo()
  elseif size == 3 then
    buildThreeByThree()
  end
end