I can only compare with England.
Most houses have cellars, old ones as well as new-builds.
Germans who want new-builds buy a plot and build it themselves, either from a prefab company or brick by brick (the prefabs are very good btw; they can be designed to your own taste). New-build house developments as occur in the UK are unheard of here.
Windows open inwards, as opposed to outwards in the UK. This is mostly to facilitate cleaning; in the UK you need to hire a window-cleaner for outside upstairs windows.
Germans like to place bedrooms up in the eaves, even though this gives some of the rooms slanting roofs. In the UK, this is usually just attic space.
Washing machines and dryers are usually in the bathroom or cellar. You won't find a washing machine in UK bathrooms; I think it's something to do with electricity, which is also why you usually have pull-strings for lights in the UK, and no ordinary sockets. UK washing machines are usually in the kitchen.
Very few carpets in German homes, and they are becoming fewer and fewer. Germans prefer tiled or wooden/laminate floors. Brits love carpets.
You'll hardly ever find a fireplace in a German house, not even in an old one. These use wood-burning stoves made of iron, or else a Kachelofen (don't know what that is in German --help me please!)
Germans like to display their names -- often full names, with names of their children as well! On their doors and doorways. In Britain, you won't find any name on the doorbell at all.
Rolläden! Germans love them on every window and glass door, and some people close up the entire house at night so that it's pitch dark in the morning. They also love their Gardinen (net curtains) so that the curious can't see in.