Stone Wall

for i=1, 1 do

turtle.select(1)
turtle.refuel(1)
turtle.up()
turtle.select(2)

for j=1, 20 do
turtle.placeDown()
turtle.forward()
end

turtle.turnLeft()
turtle.turnLeft()
turtle.up()
turtle.select(3)

for j=1, 20 do
turtle.forward()
turtle.placeDown()
end

turtle.turnLeft()
turtle.turnLeft()
turtle.up()
turtle.select(4)

for j=1, 4 do
turtle.placeDown()
turtle.forward()
turtle.forward()
turtle.forward()
turtle.forward()
turtle.forward()
end

turtle.down()
turtle.down()
turtle.down()

end