Actually Über den Wolken is also a famous song by a singer called Reinhard Mey :) It talks about watching a plane start and wishing to fly as well:
“Über den Wolken muss die Freiheit wohl grenzenlos sein. Alle Ängste, alle Sorgen – sagt man – blieben darunter verborgen, und dann würde, was uns groß und wichtig erscheint, plötzlich nichtig und klein.”
“Above the clouds freedom must know no bounds. All our fears, all our worries – they say – would stay hidden below them, and then what seems big and important to us would suddenly become trifling and small.”
It depends on what you mean.
If you mean that the birds are flying and the clouds are beneath them the whole time, then Die Vögel fliegen über den Wolken.
If you mean that the birds are flying, see a cloud, go up so that they are above the cloud and then go down again once they have crossed the cloud, then Die Vögel fliegen über die Wolken.
dem Regenbogen: masculine singular. den Wolken: plural (also Wolke is feminine but that doesn’t matter in this case because there are no gender differences in plural). So it’s the same as the difference between der Regenbogen vs. die Wolken in nominative case.
Btw, it’s über, not uber. Pay attention to umlauts; they do matter. If you can’t enter them, you should install a German keyboard and switch to that for writing German (you can do it at a keypress). And if for some reason that isn’t possible, use “ae, oe, ue” instead of “ä, ö, ü”.
Uber (with umlaut)
If you can't type an umlaut, then type an e after the vowel letter: ae oe ue Ae Oe Ue.
also means 'about'?
Yes. In that metaphorical meaning, it requires the accusative case.
- Er redet über den Wolken. "He is talking above the clouds." (dative case)
- Er redet über die Wolken. "He is talking about the clouds. (accusative case)
It can, but only in the sense of “more than” (in front of numbers): über zehn Jahre “more than ten years”. So even that one looks a lot like a preposition because it has to be followed by a number (it is not a preposition in the syntactic sense though because the head word is the number, not über).