Depends on what you plan on doing. There is a VERY good design for a flipper called the "rupt" flipper design, which takes into account a glitch in the original programming for the game. (Jimxorb created the first one, if I remember right - it's been a while since I've played.) When set up properly, a MW rupt flipper can throw an HW bot.
However, as System32 pointed out, there are no flip-out arenas in the stock version of Robot Arena, so a "pure" flipper wouldn't be much good. Additional weaponry, perhaps pop-up or hardmounted weapons, would be needed to make the bot battle-worthy.
