Using "déjà vu" as an adjective

Déjà vu is a word borrowed from French, a look into the dictionaries gives only one form, that is Déjà vu. It's a noun and seems there is no adjective form for this word. A little googling lead to this link which gives elaborate information on this word

http://sixthsensereader.org/about-the-book/abcderium-index/deja-vu/

Here it's said that the original use of the word was in adjective sense.

"Déjà vu crosswords, a little bit too Déjà vu for me"

By the above examples your sentence can be written as " Déjà vu experience". This is just like the way we use good, bad etc as adjectives ( Good experience , bad experience etc)

There is no adjectival form of déjà vu: the phrase literally means "already seen", with vu being the past particple of the verb voir, which means "to see". If you substituted the English, the correct way to incorporate it into a sentence would be "an experience already seen" (i.e., "an already seened experience" would be incorrect).

If you wanted to use it before the noun, you could rely on the listener/reader accommodating the seemingly incorrect usage of déjà vu (i.e., "a déjà vu experience") or a neologistic formation (e.g., "a dejavued experience" or "a déjà-vued experience"), but it's probably going to be clearer if you use a different adjective that conveys the same meaning as the phrase.

To this end, the word you're likely looking for is uncanny. A usage attributed to Sigmund Freud, he speaks of it thusly in "The Uncanny" (PDF):

The subject of the “uncanny” is a province of this kind. It undoubtedly belongs to all that is terrible—to all that arouses dread and creeping horror; it is equally certain, too, that the word is not always used in a clearly definable sense, so that it tends to coincide with whatever excites dread. [...] I will say at once that both courses lead to the same result: the “uncanny” is that class of the terrifying which leads back to something long known to us, once very familiar.