your own format...
1. a struct containing map information, and number of objects in the map
2. a struct containing object details like file paths
3. a struct containing irrlicht pointers for nodes
4. a vector of number 2 and a vector of number 3
write a function to fill some struct 1 and some of number 2, load the map with it (for loop through the vector using details from struct 2 to fille struct 3).
first writing the map strcutre to the file, containing to the number of objects, then for loop again writing each object of type struct 2
write a function to load this file, generating a map, then for loop loading all the object details into a vector, where you then generate your world from.
atleast thats how i did it