What is value, for Nietzsche? He's often claiming we should decide (make?) our own values, but it's not clear what that word means. Is it enough to have a genuine sense of preference for something? Because that's all I can find outside morality.
Background: You can get the essential thought in Nietzsche on value from his historical context (with Schopenhauer in behind) and four main books. (1) The Birth of Tragedy from the Spirit of Music, (2) Thus Spoke Zarathustra: A Book for All and None, (3) On the Genealogy of Morality: A Polemic and (4) Twilight of the Idols, or, How to Philosophize with a Hammer.
From these, the first concept is that the fundamental value is life and Dionysian spirit and life-affirming practices against Apollonian values and life-denying practices. The second concept is the Overman or Beyond-Man, which represents the creation/creator of new values whose ground is the death of God. Here the sense is linked to Christianity as "Platonism of the people" and Socrates rational/dialectic ideas. The corollary of the fundamental value is the supreme will to power as the human identity/essence. The third concept is the transvaluation of values (Umwertung der Werte) after using a philosophical hammer and getting a remaining value vacuum. The active nihilism will overcome the slave morality, which comes from the ressentiment and self-deception the weak has before the powerful.
Answer: The concept of value represents the determined order of a metaphysical hierarchy as explained in the first treatise in book (3) where there is an inversion of meanings of good/evil and good/bad pairs moving from a historical, aristocratic good/evil values to make its antithesis as an atemporal (beyond the deferred historicity) and imaginary power of revenge from the slavery or subjugation. This tergiversation of life as it is meant the inversion of the original hierarchy and the devaluation of historical values which turned life into something meaningless since the real power and experience are beyond this historical life. So, value here means life as it fundamentally is (existentialism) and all its moral hierarchy and its main corollary describing the human identity (personal meaning), i.e., the supreme will to power. The reason (especially from Socrates ideas) is not playing a role here. This scenario clearly puts existentialism as mostly incompatible with rationalism.
About "genuine sense of preference" and "outside morality", some prefer to summarise Nietzsche as "live as an artist (with special stress on music) and accept life as it is".
The Birth of Tragedy from the Spirit of Music Thus Spoke Zarathustra: A Book for All and None On the Genealogy of Morality: A Polemic Twilight of the Idols, or, How to Philosophize with a Hammer
What is value for Nietzsche
Anything other than Christian values (and also Islamic values - though he supposed it aligned with his. He knew very little about it).
He opposed to this - on the whole - the Epicurean notion of 'life' which he called Dionysian and the 'aristocratic' values of the ubermensch (superman/overman). These are outlined in his books beginning with his The Birth of Tragedy and ending with The Anti-Christ, after which he spent his final decade in a mental asylum.
It is worth recalling that Hitler was photographed next to Nietzsches bust, and that copies of his book, Thus spoke Zarathrustha was sent out as gifts to the German soldiers in the warfront in World War 1. He became the philosopher king of the Nazi state.
Its ironic to think that his book, The Birth of Tragedy, was prophetic in a way that was not intended by him. That is from then was dated the tragedy of the European Enlightment as it descended into a vortex of hatred and the killing fields of Europe in its two World Wars where fifty million died.
The very Anti-Christ indeed.