Act 2 scene 3 What scheme has Romeo devised?

I do not think that you have this question quite right.  Can you check and be sure that this is really the scene you want to ask about?

In this scene, Romeo talks to Friar Laurence for just a very short time.  He does not really come up with any kind of a plan.  The only thing he says that even resembles a plan is that he would like Friar Laurence to marry him and Juliet.  It's a request, but it's not much of a plan.

Are you maybe thinking of where he plans to get a rope ladder to Juliet so he will have a way to climb up to her room?

Or maybe you are thinking of the time in Act II, Scene 2, where Romeo says that Juliet should send the nurse to find him so he can tell her what the plans are for him and Juliet to get married -- this is why he's talking to the Friar in Act II, Scene 3.