Here are some places that I checked out and found suitable locations around the Messe Berlin area.
Walking distance (20-25mins usually as there's no cafe immediately nearby):
- Berliner Kaffeerösterei: I just walked by as it was a Saturday and they already closed but they have a lot of space, upstairs area. It's a 20mins walking/public transport-trip to go to Messe Berlin though.
- Cafe im Literaturhaus in the International Club Berlin. While the cafe only rents one large room within the "International Club Berlin", the club has more meeting rooms to rent. The drawback here: While the ICB is actually bordering the Messe Berlin area, there's no direct way to it, you can see the building but have to take a long detour.
- Pianocafe am Lietzensee they have a back room perfectly suited for meetups 20-30 people. <25mins walking or train distance.
S-bahn distance (around stations Charlottenburg, Savignyplatz or Bahnhof Zoo, might be even faster to get to Messe Berlin than the walking distance above. Requires a S-Bahn ticket though):
- Smoozery Berlin They are a "breakfst restaurant", run by a couple that seems very hospitable. 15mins to the south entrance of Messe Berlin, as you have the direct S-Bahn from Charlottenburg station.
- Spreeegold Bikini Berlin
- Coffee Zone nice small bar that fits 20pax into one part of the bar. No exclusive room though.
- Garage127 Coworking they have a nice community kitchen room with 140sqm to rent
More ideas:
This will be expanded further...