How can I add 100 amp electrical service to a shop?
reasons going to the service entrance will be difficult:


you'll have to open the meter box, and most meter boxes are tamper sealed by the electric company so you will have to involve them.
the meter box lugs are probably not sized for multiple connections.
this creates a potentially dangerous wiring setup. someone may assume that the main panel in the house covers the entire house.


i would go with connecting a subpanel to your main panel. i assume that the existing circuits in the shop go to the main panel? take them out and use the space you just freed up to wire in your subpanel.