To get a physical description of Romeo like we would offer today will be difficult, but you can certainly retrieve descriptions that determine his emotional appearance which shows his body language:
So early walking did I see your son:
Towards him I made, but he was ware of me
And stole into the covert of the wood:
I, measuring his affections by my own,
That most are busied when they're most alone,
Pursued my humour not pursuing his,
And gladly shunn'd who gladly fled from me.
Benvolio said this of Romeo in Act I, scene i. This shows a fleeing Romeo who hides from others. A few lines later, Montague discusses what Romeo does in his room and this further creates that emotional appearance.
In Act I, scene v, Tybalt's first words describe Romeo as having an "antic face". Then Capulet describes Romeo like this:
He bears him like a portly gentleman;
And, to say truth, Verona brags of him
To be a virtuous and well-govern'd youth
In Act II, scene ii, Juliet calls him perfect in these lines:
So Romeo would, were he not Romeo call'd,
Retain that dear perfection which he owes
Without that title.
In Act II, scene iv, Juliet is trying to discover what the Nurse found out about their upcoming marriage. The Nurse calls Romeo pretty hot stuff in these words:
face be better than any man's, yet his leg excels
all men's; and for a hand, and a foot, and a body,
though they be not to be talked on, yet they are
past compare: he is not the flower of courtesy,
but, I'll warrant him, as gentle as a lamb.
This is your best physical description. As you get further into any work, authors stray from description. They spent time in the beginning on that. So if you are going to look for more than these, I suggest Acts I and II.