A good "Kaiser" roll (or US versions of "Ciobatta") work well, but if forced to resort to the standard US "store bought" hamburger buns, toasting/frying on the "Flat Top" (or griddle in proximity to the patty (or in a bit of butter) tends to reduce "Juicy Burger Dissolution".

For "outdoor" grilled burgers made with lower fat/higher grades of beef, we often use sections of a fresh baguette, shaping the patty to fit.