About building, Tony Greenland's Panzer Modelling Masterclass is a good volume, although a bit outdated.
There are also a few Osprey books dealing with specific German tanks (Modelling the Tiger I, Modelling the Jagdpanzer 38(t) 'Hetzer', etc)
And nothing else I can remember specifically for German Tanks.
For generic model building, Adam Wilder first volume of Adam's Armour is a good one. Also the Ammo Encyclopedia volume 1.
As for painting, there are a couple of Tank Art volumes devoted to German WWII armour. And again the above Adam's Armour Volume 2 and Ammo encyclopedia, plus AK-Interative FAQ 2 deal with painting but not only about German subjects.
Hope this helps!