turtle.lua

layer = 0
maxLayer = 2
turn = 0
turtle.digDown()
while (true) do
    if turn == 0 then
        turtle.forward()
    elseif turn == 1 then
        turtle.forward()
    elseif turn == 2 then
        turtle.turnLeft()
        turtle.forward()
    elseif turn == 3 then
        turtle.forward()
    elseif turn == 4 then
        turtle.turnLeft()
        turtle.forward()
    elseif turn == 5 then
        turtle.turnLeft()
        turtle.forward()
    elseif turn == 6 then
        turtle.turnRight()
        turtle.forward()
    elseif turn == 7 then
        turtle.turnRight()
        turtle.forward()
    else
        turtle.turnLeft()
        turtle.turnLeft()
        turtle.forward()
        turtle.forward()
        turtle.turnLeft()
        layer = layer + 1
        turtle.down() 
        turn = -1
        if layer + 1 == maxLayer then
            while (true) do
                turtle.up()
                layer = layer -1
                if layer == -1 then
                    print("JOB DONE")
                    break
                end
            end
            break
        end
    end
    turtle.digDown()
    turn = turn + 1
end