Score fat layer on pork shoulder by making shallow cuts in a diamond pattern. Spread garlic, parsley, sage rosemary, and thyme over pork. Place pork in a large roasting pan, fat side up. Pour cider over pork.
Bake in the preheated oven for 8 hours. Transfer pork to a large platter; remove and discard any large pieces of fat and skin. Pour pan drippings into a separate pot. Shred meat and return to the roasting pan.
Whisk flour into water in a bowl.
Bring drippings to a boil and stir in flour mixture; cook and stir until gravy is thickened, about 5 minutes. Pour gravy over pork.