I have a rich experience with generating map tiles ready fom Google Maps API using various standards (WMTS, TMS, WMS) and at the other hand also experience with downloading them in various forms (as tiles in original file structure or as a single huge image in various formats - jpg, tiff, png, ...). As a Google Maps terms do not allow to download maps for offline use, it is possible to use another map tiles sources - like OpenStreetMaps, MapQuest, ...