Роки is the plural form of рік. "Рокі" could be a dual form, but modern Ukrainian doesnt really use dual form as language evolves and is "simplified". Most Ukrainian nouns in plural form end in either "-и" (mostly) or "-і". There are could be some rules to that but I'm not very strong on the "technical" side of things so I can't really help you with specific rules to follow.
That's an article in Ukrainian about plural forms, even though it is in Ukrainian you can see some of the examples and even observe some patterns after certain letters.
You need to copy and paste the link as duo doesn't like cyrillics in links