How do you create your levels for game dev? I guess there are many ways to do 3d level design. However, there will be a blocking in the beginning before you start with your detailed mesh. You need to plan the structure of your level and test it - again and again!
When you are finished with the blocking, it is time to start with the detailed mesh modeling... This is my personal method to do an retopology for an low-poly level design (organic structure).
Maybe there will be something which will help you as well :)