PORTAL

--0-do not replace
--1-netherrack
--2-obsidian
--3-gold
--4-diamond

myArt = {
    {0, 0, 1, 1},
    {0, 1, 1},
    {1, 1},
    {2, 2, 2, 2, 2, 2, 2, 0, 0, 0, 1, 1, 1}

}

function buildline(line)
   for i = 1,#line do
     slot=line[i]
     if slot ~= 0 then
         turtle.select(slot)
         turtle.digDown()
         turtle.placeDown()
     end
     turtle.forward()
   end
   for i=1,#line do
     turtle.back()
   end
   turtle.turnRight()
   turtle.forward()
   turtle.turnLeft()
end

for i = 1,10 do
  line = myArt[i]
  buildline(line)
end