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)
I was tired yesterday.
Updated! Thanks for the correction.
May 1, 2016
June 13, 2016
You can also use 寝たい(ねたい)
May 2, 2016
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