I love building containertrains in Transport Fever, but there aren't very many models available on Steam and TpF-forum that fits the Nordic style.
Due to the lack of suitable waggons I have tried to modify existing models from Train Fever, but have not succeeded in making them carry other types of cargo.
One of the most common waggons in containertrains here in Sweden are Lgns which are cheap and often old waggons converted from older flatwaggons.
This type was commonly used all over Europe with containers ranging in size from 20-40 feet loaded on them, but today they are for the most part replaced by more modern waggons like Sgns and Sggrs which have already been modded.
I tried searching the Internet for Blueprints and found some, but not always in German.
Link to Green Cargo, the Swedish equivalent of DB Cargo with information and measurements (Text in Swedish).
Link to DB Cargo with information and measurements (Text in German), I am thinking that German modders might feel more comfortable with this site, but can then use the drawings from the Swedish site as they provide more information.
I am thinking that the waggons could use the Cargo Asset set by Nano, Kaleut1988 and MaikC, that way I suppose You don't have to model the containers as well although their permission would of course be needed.