If i deck out my opponent can i look at there grave when they have 1 card left, so i can copy there deck and make it myself.

Short Answer: No.

Long Answer: While the graveyard is public knowledge and you are allowed to take brief notes for use in the duel, taking the time to log each and every card for later duplication would take far too long and be considered stalling. Even if you asked to check their graveyard briefly after every play to prevent stalling, that kind of tactic would be viewed dubious as well and you'd likely have a judge called over by your opponent.