To fix my roof can i just put new plywood ontop of the old?

i am trying to fix a very old plywood flat roof and i dont have a ton of money or tools. not to mention that even though the wood was cut the right way we did have to then cut it down so it would fit in my car. now when i put it back together the edges have no support beams. so i was wondering if it will really make a difference if i just put the new wood over the old and use it as more of a reinforcement? there is one area that all the plywood corners are weak so if i just put the new stuff over all 4 corners it is strong enough to hold my weight. please tell me if this ok...i dont care what it looks like as long as it is strong! i will be putting the grace sticky water and ice shield over it and then asphalt rolled roofing, and doing the patches where the connections are. is there really anything wrong with doing this?