ルームメイトがおしゃべりなのです。

roommate

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

chattering; talk; idle talk; chat; chitchat; gossip; chatty; talkative; chatterbox; blabbermouth

be; is; indicates past or completed action; indicates light imperative

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

be; is