Walls

l=27
h=100
r=1
turtle.select(1)
for u=1,h do
 turtle.up()
 turtle.placeDown()
 for t=1,4 do
  for w=1,l do
   turtle.forward()
   turtle.placeDown()
   if r<16 and turtle.getItemCount(r)<1 then
    r=r+1
    turtle.select(r)
   end
   if turtle.getItemCount(16)<1 then
     print "Out of Items"
     turtle.reboot()
    end
   end
  end
  turtle.turnRight()
 end
end