Reading Koine beyond the NT

I have primarily tried to learn Koine Greek in order to read my New Testament in the original language. However, I think my knowledge of Koine would be greatly helped by becoming more comfortable with other writings in Koine greek. Can anyone give me some helpful advice on how to increase my vocab and grasp of grammar so I can read church Fathers etc. More easily.

Thanks in advance.

You might be interested in A Patristic Greek Reader by Rodney A Whitacre. It’s designed to help biblical Greek students move ahead. Lots of explanations and vocabulary.

Thank you I will take a look.

You could also check out Reading Greek with the Desert Fathers by Timothy Brady. The Greek is slightly adapted to match the GNT in vocabulary and syntax which makes this an intermediate stepping stone between the GNT and other koine writings.