A fan-made random map generator for Heroes 5 has appeared: Tapani's HOMM V Random Map Generator (the author of the generator is Tapani Utriainen). According to the author, generating large maps takes a lot of time and requires a powerful computer for optimal performance. You can read about all the settings in the attached readme.txt file. The only drawback of the editor is that it generates maps only for 2 players, but this is version 0.7, and there may be more features in the final version, especially since the official editor, which will be included in the add-on Heroes 5: Hammers of Fate, will be released very soon.