眠たいです is a correct way to express that you're tired! You can also just say 眠いです = I am tired You can also express being tired by saying "疲れる" (つかれる) For example: 昨日私は疲れました。 I was tired yesterday. Updated! Thanks for the correction.

「眠いの」

You can also use 寝たい(ねたい)