function iff (x,y,z)
if a[x][y][z]==1 then
turtle.select(1)
elseif a[x][y][z]==2 then
turtle.select(2)
elseif a[x][y][z]==3 then
turtle.select(3)
elseif a[x][y][z]==4 then
turtle.select(4)
elseif a[x][y][z]==5 then
turtle.select(5)
elseif a[x][y][z]==6 then
turtle.select(6)
elseif a[x][y][z]==0 then
turtle.select(16)
end
end

a={{{1,2,2,1} ,
   {2,0,0,2} ,
   {2,0,0,2} ,
   {1,2,2,1}} ,

   {{1,0,0,1} ,
   {0,0,0,0} ,
   {0,0,0,0} ,
   {1,0,0,1}} ,

   {{1,0,0,1} ,
   {0,0,0,0} ,
   {0,0,0,0} ,
   {1,0,0,1}} ,

   {{1,2,2,1} ,
   {2,0,0,2} ,
   {2,0,0,2} ,
   {1,2,2,1}} ,
}

turtle.up()

for x=1, #a do
  for y=1, #a[x] do
    for z=1, #a[x][y] do
      iff(x,y,z)
      turtle.placeDown()
      turtle.forward()
    end

turtle.turnRight()
turtle.forward()
turtle.turnRight()

for y = 1,#a[x][y] do
turtle.forward()
end

turtle.turnRight()
turtle.turnRight()
end

turtle.turnLeft()
for y = 1,#a[x] do
turtle.forward()

end
turtle.turnRight()
turtle.up()
end