In Shakespeare's romantic tragedy, the complication is the meeting of Romeo and Juliet in Act I, Scene 5. This is the catalyst that starts the major conflict. The resolution occurs after Prince Escalus summons Lord Capulet and Lord Montague in Act 5, Scene 3. The parents are informed of the events involving the deaths of Romeo and Juliet; afterwards, they reconcile and end their feud.
In Act I, Scene 5, Romeo decides to follow the suggestion of Benvolio that they enter the Capulet ball and then leave. However, he sees Juliet and becomes love-struck. As he speaks to himself of Juliet's beauty, Tybalt hears him and recognizes his voice as that of a hated Montague. Enraged, he sends for his sword. But Lord Capulet wants no violence on this night of celebration, so he tells Tybalt, "He shall be endured" (1.5.74). Tybalt departs.
Then, Romeo approaches Juliet and speaks to her in loving terms; she replies with more restraint. Undeterred, Romeo kisses her. Afterwards, Romeo learns that Juliet is a Capulet, and he exclaims, "my life is my foe's debt" (1.5.118). Here the dramatic entanglement, or complication, has begun.
In Act V, Scene 3, the resolution, or the set of events that bring the play to its end, occurs.
After being sent for by the watchmen in the early morning, Prince Escalus is informed by Balthasar, Friar Lawrence, and the Page for Count Paris of the events that have occurred. He summons the Capulets and Lord Montague, and they are given the tragic news.
With their beloved children now dead, the Capulets reconcile with Lord Montague, whose wife has died of grief over Romeo's banishment. Prince Escalus declares that "all are punish'd" (5.3.306) because of the feud. Finally, Lord Capulet offers Lord Montague his hand in peace, and Lord Montague promises to erect a statue of Juliet in pure gold. The Prince concludes the affair as he remarks on what a tragic story of woe that of Romeo and Juliet has been. These are the set of events that bring the drama to its close.
Romeo and Juliet is chockfull of complications, the most central one being the relationship between Romeo Montaque and Juliet Capulet. The Montaques and the Capulets have been "at war" for years, yet it didn't stop Romeo and Juliet from falling in love. Because of the situation between the families, Romeo and Juliet's relationship has very little chance of being accepted by the families, so they decide to sneak off and elope. Unfortunately, their plan backfires because of miscommunication, resulting in a double suicide. The one positive resolution stemming from this tragedy is the end of the long-standing war between the Montaques and the Capulets. This "cease fire" paves the way for a future of peace between two families, a peace that most likely would never have happened without having the "wakeup call" resulting from this tragic event.
I wouldn't apply a plot diagram to this play, which (I think) is what this question is asking. If so, the building action would be all of the events leading up to the climax (the two deaths), the resolution would be the final scene where the explanations and peace offerings are made, and the complications would be in the scene we don't see where the friar is detained on route to Romeo and where Romeo hears (incorrectly) that Juliet is dead.