Well first of all, I don't know if you aim for a modern Germany or Project Zomboid lore accurate 1993 Germany. This would change some things.
Some of those things you guys may already did, but I don't remember everything of the map, so if something on the list is already done, just ignore it.


First of all, the buildings will already do a lot.

• Most residental homes are made of bricks, followed by cement, followed by lime stone and wood. Wood is often used as a facade and applied in a hybrid material build. If not repainted most houses also tend to be either white or yellow.
  
• Project Zomboid's default windows are all typical American, where you can slide them open. If you aim for German windows you should add custom ones, like some in Dinkerdam, which can be opened horizontially.
  
• Solar panels are a more modern Germany thing. If you aim for a nowadays Germany you should add solar panels to around 12% of the residential houses, because this should be the real life staticial number. If you aim for the 1993 feel, almost none should have them.
  
• Speaking of roofs btw: Commons colors should be red/orange, black and gray. As far as I noticed, I think you already avoided that: But avoid flat roofs. Very very uncommon and mostly only used on Plattenbauten (but even some of those have a slightly angled roofs) or some standalone shops.
  
• Germany doesn't use those American mailboxes the game provides. Our mail boxes are very often real boxes attached to either the fence of the lot, the house wall (where they can sometimes be opened from inside the house) or in cases of those apartment buildings they're literal boxes standing in front of the building with a smaller box for each apartment/family.
  
• When Germans own garages there are two types. Either those garages that are a seperate small building either a bit to the side or in the backyard of the house or attached to the main house, where as the garage roof is not as steap as the main houses roof.
  
• Some smaller clutter like drains for the rain water.
  
• Balconies, especially on Apartment building are quite a common sight.
  
• For when you reach East Germany: The DDR used a lot of standartized houses when rebuilding the country. You can basically look up things like: EW 58, reconstruct them ingame and design some variants of them and already cover like 500.000 East German residental homes. Also Plattenbauten. Very common over here.
  
• Not quite sure how common it is in the west, but East Germans love their carpets with patterns on them.

• You could include various real life stores that are quite common in Germany: Netto, Edeka, Lidl, Aldi, Real, Fielmann, Apotheke, C&A, Kik, H&M, OBI, IKEA, Rossmann, DM, ... If you aim for the 90s don't forget some older buisnesses that went out of buisness like Schlecker, Hallo Pizza and many more.
  
• Besides those big chains there are also a lot of bakeries, kebab shops and those asian restaurants that are maintained by some vietnamese while they also offer japanese food (plus points if they're named something with either Bambus or Wok in their name). For a modern Germany you can also include some bubble tea shops and shisha bars.
  
• Fire exits. Due to fire safety regulations those buildings need to have several doors leading to the outside. For your average super market or whatever, they might not often be that super obvious, but they're there. Often thick doors. Also don't forget those fire exit signs above or near them.
  
• Chairs at cash registers of super markets.
  
• If the shop isn't restocking daily (or multiple times a day), then do not forget a storage area attached to it somewhere in the back.
  
• As someone who once worked in a Netto: Pfand put into those Pfandautomaten are sorted in the back with some converyor belt. At the time I worked there (around 2010 or 2011) glass was sorted manually, while plastic bottles were automatically put into bins with big plastic bags.
  
• If workers of the place wear any kind of work uniform, they also have very likely some closets in the employees only area (which also should feature a toilet, perhaps a small office and a break room at least)

• Very common and shouldn't be forgotten. While America tends to really seperate them, it's not quite uncommon to have some apartments right above an shop, restaurant, drugstores or sometimes even family doctors.

• Old towns tend so use a bit more decoration on the buildings.
  
• Fachwerkshäuser, especially in villages around middle Germany.

• Germany loves it's traffic regulations. So put street signs everywhere. Stop signs, One way roads, (Non-)Parking Zones, etc.
  
• Public transport! Do not forget bus stops and for bigger cities also include tram lines. For build 42 when basements and road ramps drop: Those passages where rails are above the road or the other way around. Also subways in some bigger cities like Berlin. Oh and the Autobahn tend to be elevated too.
  
• Car spawns should be applied to the side of many roads. Parking at the sidewalk is quite common unless banned for this particular street by any traffic regulation.
  
• Alleys with trees to the side of the road. Obviously not everywhere but it's quite common European.
  
• Different colored trash bins for different types of trash.
  
• Sound barriers to the side of the Autobahn, guarding rails on the Autobahn and those reflector posts each 50m (or less, if the road is quite curvy) on roads outside of cities.
  
• Include curvy roads in the city. I know this is harder to do, as houses can only face 4 directions, but apply where it is possible to avoid straight grids in the cities.
  
• Bike lanes on the pavement.
  
• Random street clutter: electrical boxes, benches, advertisment signs on walls or smaller advertisment signs for shops right in front of them, mail boxes and if you go for 90s Germany than do not forget the typical yellow telephone boxes or the white Telekom ones.

• Germany has harsh gun laws, so perhaps reduce gun spawn rates. Guns should rather be found at police stations and military bases. Guns shouldn't be completly be removed from residential buildings, but a lot rarer and and especially should mostly be pistols. Assault rifles are not buyable for a private person.
  
• If you're going for a 90s Germany and are able to create own clothings/retextures: The green and yellowish police uniforms. And green police cars.
  
• If you guys ever go to create custom vehicles as well: Do not forget all those German car brands like VW, BMW, Audi, Opel, Mercedes, etc.

• NATO had and has a lot of military bases further from the former East German border. They we're place further away from it, so that in a case of an eastern invasion, they wouldn't directly fall and possibly provide the enemy with more weapons.
  
• The US has also still a lot of military bases in Germany including Bavaria, Baden Wüttemberg, NRW, Rheinlandpfalz, Saarland and Hessen. The information is public enough to be found on Wikipedia. Though considering the current area covered the next one would be somewhere around Obergammerau.
  
• While West German lanterns tend to shine in blueish/white colors due to using mercury vapor or metal halide, East German lanterns tend to shine in yellowish/orangish colors as they were using sodium vapor. A transitiont of the later ones is happening, but it's ongoing very very slow and the difference can still be seen from space - especially in Berlin where both clash against each other.

@TitanKämpfer, thanks for the advice! Of course, my reply comes almost a year later due to the project being put on hold, but I’ve read everything carefully, and now we’ll try to implement all of it.

For now, using the in-game windows and mailboxes is more of a temporary solution, as adding such tiles to the map is still difficult due to a lack of knowledge and experience—we're still beginners when it comes to map creation. However, tips like using orange roof tiles and non-flat roofs have already been actively applied. We've also added solar panels to rooftops, though unfortunately, they are purely visual for now, as we still lack the skills to create fully functional mods.

We've implemented shop signs and road signs, but we missed a few—thanks to your comment, I'll make sure to add them too. (We haven’t placed them yet, but they’ll definitely be included in the next update.)

Balconies somehow slipped my mind, so thanks a lot for that suggestion! Separate garages instead of built-in ones are also something I’ll take into account. That said, in my city, around 90% of garages are integrated into buildings, which is why I originally designed them that way, but I’ll definitely consider this for future updates.

Different bakeries and kebab shops are a great idea for variety, and they will definitely be added.

As for fire exits, newer buildings already have "Exit" signs, which indicate emergency exits as we use them, but if I missed some, I’ll look up more references and add new ones.

Regarding Pfandautomaten, I actually worked a mini-job at Penny and know about these sorting machines. While I think they’re a nice detail that could be added later, I personally feel they’re not a priority right now (just my subjective opinion).

Uniforms—unfortunately, I don’t yet know how to add uniforms or clothing, as that would require modding. If anyone has suggestions or knows of helpful resources, feel free to share!

Hybrid buildings—I assume you mean buildings where the lower floors have pharmacies, shops, etc., while the upper floors contain apartments or offices? This wasn’t implemented in the initial buildings, but we’ve started using this concept extensively in the new city.

Bus stops, bike lanes, advertisements—great ideas, I’ll make sure to add them! They will definitely bring more life to the map. Also, military structures like NATO and US bases will definitely be included.

Many of the older buildings and structures no longer meet our new construction standards, but we’ll do our best to update and improve them.

Sorry for the late response, but I really appreciate your ideas and suggestions—they will help improve the project significantly!

Great to hear the project is still kicking in some way. I have a German map and accompanying mods myself I'm working on (though mine is entirely set in a fictional region of Germany, to allow for a bit more freedom), but is currently also on hold.

For windows I can recommend you checking out Melos tilesets on the Steam workshop. He has tons of tiles for everyone to use and it definitely will have some tiles useful for your project, for example some windows that would definitly fit a bit more into a European scenery. Also roofs with other slope angles, which will help you avoid going for roofs too steep.

I know you guys aimed for a recreation of places, so if the towns you recreated have the garages attached to the houses, stay with that. Makes more sense for a recreation, right? The seperated garages is something that I've just observed in my surroundings and German architecture obviously will have variance between it's states and regions.

If you guys need any help, you can hit me up.