Use the adjective shapely to describe someone whose body has an attractive shape. You might start going to the gym to run and lift weights with the goal of becoming more shapely.
The word shapely most often describes a woman, but there's no reason you can't use it to talk about a nicely shaped man as well. You could describe a mountain climber you know as being physically fit, with shapely legs, or complain that fashion magazines are full of identical shapely models, with no variation of body types. Shapely has been used in English since the fourteenth century, from the Old English root word gesceap, or "creation, form, or destiny."