We just tried this for supper tonight, and I'd say it's pretty close to the taste of Arby's. As usual, I took the original recipe and tweaked it to better suit our tastes-- here's my version:
Amy's Copycat Arby's Roast Beef Sandwiches
1 lb. of deli roast beef
1 tablespoon brown sugar
1/2 cup of ketchup
1/4 cup water
1/4 tsp yellow mustard
a dash of each: salt, pepper, and chili powder
Combine all sauce ingredients into a large skillet over medium heat. While sauce simmers, cut roast beef into strips (I did this before seperating the slices). Stir roast beef into sauce and simmer until warmed through. Serve on hamburger buns.
I got five sandwiches out of this, but they weren't piled too high. If you want bigger sandwiches or are feeding several adults, I'd suggest doubling the recipe.
Fast food taste at a much smaller cost... that definitely works for me!