Help me modify someone else's code!

-- Made By Orwell
-- version 0.2 - 3 june 2012

local tArgs = { ... }
if #tArgs ~= 1 then
  print("Usage: build <gunzipped schematic file>")
  return
end

local filename = tArgs[1]

if not fs.exists(filename) then
  print("File does not exist.")
  return
end

local length = 0
local height = 0
local width = 0
local blocks = {}
local data = {}

block_id = {}

block_id[0] = "Air"
block_id[1] = "Stone"
block_id[2] = "Grass"
block_id[3] = "Dirt"
block_id[4] = "Cobblestone"
block_id[5] = "Wooden Plank"
block_id[6] = "Sapling"
block_id[7] = "Bedrock"
block_id[8] = "Water"
block_id[9] = "Stationary water"
block_id[10] = "Lava"
block_id[11] = "Stationary lava"
block_id[12] = "Sand"
block_id[13] = "Gravel"
block_id[14] = "Gold Ore"
block_id[15] = "Iron (Ore)"
block_id[16] = "Coal Ore"
block_id[17] = "Log"
block_id[18] = "Leaves"
block_id[19] = "Sponge"
block_id[20] = "Glass"
block_id[21] = "Lapis Lazuli (Ore)"
block_id[22] = "Lapis Lazuli (Block)"
block_id[23] = "Dispenser"
block_id[24] = "Sandstone"
block_id[25] = "Note Block Tile entity"
block_id[26] = "Bed"
block_id[27] = "Powered Rail "
block_id[28] = "Detector Rail "
block_id[29] = "Sticky Piston"
block_id[30] = "Cobweb"
block_id[31] = "Tall Grass"
block_id[32] = "Dead Bush"
block_id[33] = "Piston"
block_id[34] = "Piston Extension"
block_id[35] = "Wool"
block_id[36] = "Block moved by Piston"
block_id[37] = "Dandelionandelion"
block_id[38] = "Rose"
block_id[39] = "Brown Mushroom"
block_id[40] = "Red Mushroom"
block_id[41] = "Block of Gold"
block_id[42] = "Block of Iron"
block_id[43] = "Double Slabs"
block_id[44] = "Slabs"
block_id[45] = "Brick Block"
block_id[46] = "TNT"
block_id[47] = "Bookshelf"
block_id[48] = "Moss Stone"
block_id[49] = "Obsidian"
block_id[50] = "Torch"
block_id[51] = "Fire"
block_id[52] = "Monster Spawner"
block_id[53] = "Wooden Stairs"
block_id[54] = "Chest"
block_id[55] = "Redstone (Wire)"
block_id[56] = "Diamond (Ore)"
block_id[57] = "Block of Diamond"
block_id[58] = "Crafting Table"
block_id[59] = "Seeds"
block_id[60] = "Farland"
block_id[61] = "Furnace"
block_id[62] = "Burning Furnace"
block_id[63] = "Sign Post"
block_id[64] = "Wooden Door"
block_id[65] = "Ladders"
block_id[66] = "Rails"
block_id[67] = "Cobblestone Stairs"
block_id[68] = "Wall Sign"
block_id[69] = "Lever"
block_id[70] = "Stone Pressure Plate"
block_id[71] = "Iron Door"
block_id[72] = "Wooden Pressure Plates"
block_id[73] = "Redstone Ore"
block_id[74] = "Glowing Redstone Ore"
block_id[75] = "Redstone Torch"
block_id[76] = "Redstone Torch"
block_id[77] = "Stone Button "
block_id[78] = "Snow"
block_id[79] = "Ice"
block_id[80] = "Snow Block"
block_id[81] = "Cactus"
block_id[82] = "Clay (Block)"
block_id[83] = "Sugar Cane"
block_id[84] = "Jukebox"
block_id[85] = "Fence"
block_id[86] = "Pumpkin"
block_id[87] = "Netherrack"
block_id[88] = "Soul Sand"
block_id[89] = "Glowstone"
block_id[90] = "Portal"
block_id[91] = "Jack-O-Lantern"
block_id[92] = "Cake Block"
block_id[93] = "Redstone Repeater"
block_id[94] = "Redstone Repeater"
block_id[95] = "Locked Chest"
block_id[96] = "Trapdoors"
block_id[97] = "Hidden Silverfish"
block_id[98] = "Stone Brick"
block_id[99] = "Huge brown and red mushroom"
block_id[100] = "Huge brown and red mushroom"
block_id[101] = "Iron Bars"
block_id[102] = "Glass Pane"
block_id[103] = "Melon"
block_id[104] = "Pumpkin Stem"
block_id[105] = "Melon Stem"
block_id[106] = "Vines"
block_id[107] = "Fence Gate"
block_id[108] = "Brick Stairs"
block_id[109] = "Stone Brick Stairs"
block_id[110] = "Mycelium"
block_id[111] = "Lily Pad"
block_id[112] = "Nether Brick"
block_id[113] = "Nether Brick Fence"
block_id[114] = "Nether Brick Stairs"
block_id[115] = "Nether Wart"
block_id[116] = "Enchantment Table"
block_id[117] = "Brewing Stand"
block_id[118] = "Cauldron"
block_id[119] = "End Portal"
block_id[120] = "End Portal Frame"
block_id[121] = "End Stone "
block_id[256] = "Iron Ingotron Shovel"
block_id[257] = "Iron Pickaxe"
block_id[258] = "Iron Axe"
block_id[259] = "Flint and Steel"
block_id[260] = "Red Apple"
block_id[261] = "Bow"
block_id[262] = "Arrow"
block_id[263] = "Coal"

woolColors = {}
woolColors[0] = "White"
woolColors[1] = "Orange"
woolColors[2] = "Magenta"
woolColors[3] = "Light Blue"
woolColors[4] = "Yellow"
woolColors[5] = "Lime"
woolColors[6] = "Pink"
woolColors[7] = "Gray"
woolColors[8] = "Light Gray"
woolColors[9] = "Cyan"
woolColors[10] = "Purple"
woolColors[11] = "Blue"
woolColors[12] = "Brown"
woolColors[13] = "Green"
woolColors[14] = "Red"
woolColors[15] = "Black"

function getBlockName(id, blockData)
  blockData = blockData or nil
  if(block_id[id] == nil) then
	return "UNKNOWN"
  else
	if(blockData) then
	  if(id == 35) then
		str = woolColors[blockData] .. " " .. block_id[id]
		return str
	  end
	end
	return block_id[id]
  end
end

function getBlockId(x,y,z)
  return blocks[y + z*width + x*length*width + 1]
end

function getData(x,y,z)
  return data[y + z*width + x*length*width + 1]
end

function readbytes(h, n)
  for i=1,n do
	h.read()
  end
end

function readname(h)  
  n1 = h.read()
  n2 = h.read()

  if(n1 == nil or n2 == nil) then
	return ""
  end

  n = n1*256 + n2

  str = ""
  for i=1,n do
	c = h.read()
	if c == nil then
	  return
	end  
	str = str .. string.char©
  end
  return str
end

function parse(a, h, containsName)
  containsName = containsName or true
  if a==0 then
	return
  end
  if containsName then
	name = readname(h)
  end

  if a==1 then
	readbytes(h,1)  
  elseif a==2 then
	i1 = h.read()
	i2 = h.read()
	i = i1*256 + i2
	if(name=="Height") then
	  height = i
	elseif (name=="Length") then
	  length = i
	elseif (name=="Width") then
	  width = i
	end
  elseif a==3 then
	readbytes(h,4)
  elseif a==4 then
	readbytes(h,8)
  elseif a==5 then
	readbytes(h,4)
  elseif a==6 then
	readbytes(h,8)
  elseif a==7 then
	i1 = h.read()
	i2 = h.read()
	i3 = h.read()
	i4 = h.read()
	i = i1*256*256*256 + i2*256*256 + i3*256 + i4
	if name == "Blocks" then
	  for i=1,i do
		table.insert(blocks, h.read())
	  end
	elseif name == "Data" then
	  for i=1,i do
		table.insert(data, h.read())
	  end
	else
	  readbytes(h,i)
	end
  elseif a==8 then
	i1 = h.read()
	i2 = h.read()
	i = i1*256 + i2
	readbytes(h,i)
  elseif a==9 then
   --readbytes(h,5)
   type = h.read()
   i1 = h.read()
	i2 = h.read()
	i3 = h.read()
	i4 = h.read()
	i = i1*256*256*256 + i2*256*256 + i3*256 + i4
	for j=1,i do
	  parse(h.read(), h, false)
	end
  end
end

function forward()
  while not turtle.forward() do
	turtle.dig()
  end
end

function up()
  while not turtle.up() do
	turtle.digUp()
  end
end

function down()
  while not turtle.down() do
	turtle.digDown()
  end
end

function place()
  while not turtle.placeDown() do
	turtle.digDown()
  end
end

h = fs.open(filename, "rb")

a = 0
while (a ~= nil) do
  a = h.read()
  parse(a, h)
end

write("length: " .. length)
write("   width: " .. width)
write("   height: " .. height .. "\n")

uniqueblocks={}
for i,v in ipairs(blocks) do
  found = false
  for j,w in ipairs(uniqueblocks) do
	-- for now, data is only accounted for when the block is whool
	if (w.blockID==v and (w.data==data[i] or w.blockID ~= 35)) then
	  found = true
	  w.amount = w.amount + 1
	  break
	end
  end

  if found==false then
	uniqueblocks[#uniqueblocks+1] = {}
	uniqueblocks[#uniqueblocks].blockID = v
	uniqueblocks[#uniqueblocks].data = data[i]
	uniqueblocks[#uniqueblocks].amount = 1
  end
end

print("number of block types: " .. #uniqueblocks)
for i,v in ipairs(uniqueblocks) do
  if (i%9)==0 then
	read()
  end
  print(" -" .. getBlockName(v.blockID, v.data) .. ": " .. v.amount)
end

read()

print("Give the numbers of all slots containing the specified block type:")

slots={}
for i,block in ipairs(uniqueblocks) do
  blockData = block.data
  print(" -in which slots is " .. getBlockName(block.blockID, blockData) .. "?")
  if not slots[block.blockID] then
	slots[block.blockID] = {}
  end
  slots[block.blockID][blockData] = {}
  write("   ")
  str = read()
  for i = 1, #str do
	local c = str:sub(i,i)
	n = tonumber©
	if(n) then
	  if(n>0 and n<17) then
		table.insert(slots[block.blockID][blockData], n)
	  end
	end
  end
end

print("Press key to start building...")
read()

up()
n = 1
turtle.select(n)

for x=1,height do
  for y=1,width do
	for z=1,length do
	  blockID = getBlockId(x-1,y-1,z-1)
	  blockData = getData(x-1,y-1,z-1)
	  forward()
	  turtle.digDown()
	  slot_lst = slots[blockID][blockData]
	  if(slot_lst ~= nil) then
		if(#slot_lst > 0) then
		  local found=false
		  for i,v in ipairs(slot_lst) do
			if(turtle.getItemCount(v) > 0) then
			  found=true
			  turtle.select(v)
			  break
			end
		  end
		  if not found then
			print("Not enough " .. getBlockName(blockID, blockData) .. ". Please refill...")
			read()
		  end
		  place()
		end
	  end
	end
	turtle.turnLeft()
	forward()
	turtle.turnLeft()
	for i=1,length do
	  forward()
	end
	turtle.turnRight()
	turtle.turnRight()
  end
  turtle.turnRight()
  for i=1,width do
	forward()
  end
  turtle.turnLeft()
  up()
end

for i=1,height+1 do
  down()
end