Make a simple data structure (like a struct with 2 arrays or something simple), then release a specification for the file format, you may want to look at other specifications to have a Idea of possible problems. Then provide to users a simple header only library (C or C++ 03) they can use to convert the data structure into a file using 1 function.
Cover simpler functionality first, if you want to support huge worlds your file format is likely to need an "index" as header that points to location of chunks like an archive.
Make it extendible (by leaving some encode space free for extensions) so that if it become successfull you can help users support even more cool content. You can also make some few importers/exporters for popular languages (Java and C#) but be precise with specifications so everyone can contribute.
Junior Irrlicht Developer.
Real value in social networks is not about "increasing" number of followers, but about getting in touch with Amazing people.
- by Me