Rooms are JSON - you can see what it has generated in the script/file and access it yourself as you may,
var _x_ini_node = 2016;
repeat (3) {
var json_rooms = scr_room_node(); // generated from rooms starting with rt_
// pick a random room name from the map:
var name = ds_map_find_first(json_rooms);
repeat (irandom_range(0, ds_map_size(json_rooms) - 1)) {
name = ds_map_find_next(json_rooms, name);
}
// and load that:
var _room = json_rooms[?name];
room_pack_load_map(_room, _x_ini_node, 0, room_pack_flag_instances);
var _roomSettings = _room[?"roomSettings"];
_x_ini_node += _roomSettings[?"Width"];
}
// and when you're done:
ds_map_destroy(json_rooms);