There won't be tons of drippings from the roast, but pour off any that there is, fat included, scraping up any little browned bits, too. When adding to the broth, you may want to strain it before you add the thickener.
homemade turkey stock is best, if you have it on hand, if not, store-bought (gluten-free) will work, too.
gravy thickened with arrowroot can tend to be a tad thin, when reheated. You may need to add additional starch with any leftovers