-- Function to select a slot with blocks
function selectBlock()
  for i = 1, 16 do
    if turtle.getItemCount(i) > 0 then
      turtle.select(i)
      return true
    end
  end
  return false
end

-- Fill platform of given width and length
function fillPlatform(width, length)
  local turnRight = true

  for row = 1, length do
    for col = 1, width do
      if not selectBlock() then
        print("Out of blocks!")
        return
      end
      turtle.placeDown()
      if col < width then
        turtle.forward()
      end
    end

    if row < length then
      if turnRight then
        turtle.turnRight()
        turtle.forward()
        turtle.turnRight()
      else
        turtle.turnLeft()
        turtle.forward()
        turtle.turnLeft()
      end
      turnRight = not turnRight
    end
  end
end

-- Replace these with desired dimensions
local width = 5
local length = 4

-- Start the filling
fillPlatform(width, length)