Hi Tomek,
Of course you can create your own maps. All that you need is the OsmAndMapCreator program, a proper JAVA Runtime Environment... and a PC with *a lot* of memory (depending on how big is the raw file you're processing).
However, I don't think generating one single, huge .obf file is (anymore) necessary: when the old search algorithm was used, this was a major issue since the search would only take place only on the map you specified (you were forced to know in advance in which package the searched location was).
The current search routine, instead, looks into every active map present in your device, so there's no difference in having one comprehensive map or many regional maps installed.
Cheers,
Max