What is the original appearance and sound of the Nicene Creed? There are numerous places on line where one can see the modern Greek text of the creed and hear it read.  I would like to know how differently the original 4th century text would appear in a contemporary manuscript, and how differently it would sound if verbalised by one of the original authors.
Disclaimer: I am neither linguist or a Greek. 

Since Koine Greek was used in that era, you could compare it with the current language rules.

There are two versions: Creed of 325
and Constantinople Creed of 381
so you are probably looking for original version. 

Original (325) Greek version:


  Πιστεύομεν εἰς ἕνα Θεὸν Πατέρα παντοκράτορα
      πάντων ὁρατῶν τε καὶ ἀοράτων ποιητήν·
      καὶ εἰς ἕνα Κύριον Ἰησοῦν Χριστὸν
      τὸν Υἱὸν τοῦ Θεοῦ,
      γεννηθέντα ἐκ τοῦ Πατρὸς μονογενῆ
      τουτέστιν ἐκ τῆς οὐσίας τοῦ Πατρος
      Θεὸν ἐκ Θεοῦ,
      Φῶς ἐκ Φωτός,
      Θεὸν ἀληθινὸν ἐκ Θεοῦ ἀληθινοῦ,
      γεννηθέντα, οὐ ποιηθέντα,
      ὁμοούσιον τῷ Πατρί,
      δι’ οὗ τὰ πάντα ἐγένετο
      τά τε ἐν τῷ οὐρανῷ καὶ τὰ ἐν τῇ γῇ,
      τὸν δι’ ἡμᾶς τοὺς ἀνθρώπους, καὶ
      διὰ τὴν ἡμετέραν σωτηρίαν,
      κατελθόντα,
      καὶ σαρκωθέντα,
      καὶ ἐνανθρωπήσαντα,
      παθόντα,
      καὶ ἀναστάντα τῇ τρίτῃ ἡμέρᾳ,
      ἀνελθόντα εἰς τοὺς οὐρανούς,
      ἐρχόμενον κρῖναι ζῶντας καὶ νεκρούς.
      καὶ εἰς τὸ Ἅγιον Πνεῦμα.
      Τοὺς δὲ λέγοντας Ἦν ποτε ὅτε οὐκ ἦν,
      καὶ Πρὶν γεννηθῆναι οὐκ ἦν,
      καὶ ὅτι Ἐξ οὐκ ὄντων εγένετο,
      ἢ Ἐξ ἑτέρας ὑποστάσεως ἢ οὐσιάς φάσκοντας εἶναι
      ἢ κτιστόν
      ἢ τρεπτόν
      ἢ ἀλλοιωτὸν τὸν Υἱὸν τοῦ Θεοῦ,
      τούτους ἀναθεματίζει ἡ ἁγία καθολικὴ καὶ ἀποστολικὴ ἐκκλησία.  


English translation of the 325 version:


  We believe in one God,
      the Father almighty,
      maker of all things visible and invisible;
      And in one Lord, Jesus Christ,
      the Son of God,
      begotten from the Father, only begotten,
      that is, from the substance of the Father,
      God from God,
      light from light,
      true God from true God,
      begotten not made,
      of one substance with the Father,
      through Whom all things came into being,
      things in heaven and things on earth,
      Who because of us men and because of our salvation came down,
      and became incarnate
      and became man,
      and suffered,
      and rose again on the third day,
      and ascended to the heavens,
      and will come to judge the living and dead,
      And in the Holy Spirit.
      But as for those who say, There was when He was not,
      and, Before being born He was not,
      and that He came into existence out of nothing,
      or who assert that the Son of God is of a different hypostasis or substance,
      or created,
      or is subject to alteration or change. 
      - these the Catholic and apostolic Church anathematizes.


Here is comparison between 352 and 381 versions.

All I could find was this video claiming to be in Koine Greek: ΤΟ ΣΥΜΒΟΛΟΝ ΤΗΣ ΠΙΣΤΕΩΣ (The Symbol of Faith)