"It is never clean in his room."
Translation:W jego pokoju nigdy nie jest czysto.
"Czysto" is an adverb. "Czyste" is an adjective and it would have to describe some neuter or non-masculine-personal noun, the word "to" or pronoun "ono".
If you are going to use a long sentence, first practice half beforehand. We essentially have to guess the whole sequence, and then somehow memorise the whole thing to repeat it. One reason you suceeded at school in languages is your ability to memorise. One reason many failed to do so is not laziness but the inability to memorise at your level. When you teach people like us, whatever worked for you is probably going to fail us as much as it did at school. Long sentences are not going to work well enough often enough without a better structured approach.
And... when you keep having to retype the whole thing again and again you lose confidence in your ability or to take risks. Now here is something interesting: where i work the people who try their English on me or others are most worried that we are evaluating their English. We are not, our job is to rewrite EN texts. When we ask why they are so concerned they all say it is because their teachers instilled that self doubt. Maybe tradition has to change. Maybe teaching needs more cinsideration of the student, not as a grammar engine but as people with different learning strategies.
I don't believe that there is such a sentences containing "nigdy", but without "nie". Unless it's a one word sentence. But even then it means "never".
So does the construction sometimes mean "not ever"? Nigdy is defined as never or ever (when I use the translation function by clicking on the underlined word).