Depends. If you're an artist like me, then it'll be a piece of cake. If you are an artist but you draw something else, or you don't draw at all, then this will be a bit tough. I suggest you get into the games more before you draw. If you've been playing for a long time, then start off with tracing vectors and such. Then eventually you'll receive your own art style. That, and maybe an art community place like Deviantart can help you. DragoArt is good too, for beginners. I hope this helped :)
Two Sonic Heroes sites would be www.sega.com/gamesite/sonicheroes/content.html and www.toughteam.com/. The three main characters feature on the main page itself. Choose wallpapers and sketch the same. Check out various sonic heroes screen shots. Look up team sonic, team rose or even team dark and team chaotix.
Sonic Heroes essentially refers to a video game which features in the Sonic the Hedgehog popular series. The game is prided as the earliest multi platform game seen in the Sonic series.