Have you already tried to make a slab pie? This may not be a very nice name for what is simply a large pie made on a cookie sheet (the large kind with a lip, called a jelly-roll pan). It can also be baked in a casserole dish.
There’s no science to making this type of pie. Just as you use the same dough-to-filling ratio for mini or hand pies, the same applies for the slab. As this is usually a pie to feed a large group of people, double the recipe. Or maybe even triple it. Then, you may not be able to put your over-sized dough into the dish without breaking it. If this is the case, use a paring knife to cut the dough into manageable pieces and arrange them evenly in the dish. Add the topping and cover with top crust. You can cut a decorative pattern on top. A lattice top looks very nice; use extra-wide strips of dough to save time.