The official Roger Federer logo was designed by Dael Brasil according to brands of the world.com. However, if you search for this name it produces no relevant results and it is not mentioned anywhere else. The best way to confirm who the designer is, would be to contact Federer's official website and ask directly. You could even find that he designed it himself. He has said that he likes the logo as a way of connecting with fans.

It's unusual for a tennis player to have his or her own logo, and Roger Federer's distinctive design has attracted quite a lot of attention. Not all of this is admiring - a lot of people working in design and fashion think that, although he is a well dressed man, his logo isn't very impressive. However, he probably has more important things to think about, like winning yet another Wimbledon title next year...