The Flakpanzer IV "Wirbelwind" (whirlwind in english) was a German self-propelled anti-aircraft gun based on the Panzer IV tank. Instead of the normal Pz IV turret, an open-top turret with four 20 mm autocannons was installed (Wikipedia).
The outside shape of the turret is pretty accurate, as there is plenty of reference material available online. However, the inside of the turret and the guns themselfs are mostly guesswork. For reference material I had to rely on images from other model kits and then tried my best to come up with a reasonable looking gun assembly. All in all I'm quite happy with the result and best thing is, that the guns and the optics can pivot up and down.
The tank hull and the tracks are from m_bergman's fantastic collection. I scaled everything up to 1/56, cleaned up the hull a bit and separated the tracks for easier printing. If you prefer to print the hull with the tracks attached, I'd recommend getting the original file from m_bergman.
I'd also recommend using metal rods for the gun barrels, because the parts become very fragile if printed (if the print at all...). Aluminium or brass works well. I used Ø1.3 mm rods and cut them to 27 mm in length. If you use metal rods, don't forget to print a muzzle for each gun.
For the pins, which connect the optics to the guns, I also used metal parts. I clipped Ø0.9 mm nails to size and glued them on. I still included a model of the pin in the download files for reference purposes, but don't bother printing those...
Please note, that some of the gun parts are quite small and may require multiple prints until a nice result is achieved.