Well, that question depends on the lady.
I personally don't find well-built guys that attractive. Steroids and loads or gym time do not sound handsome and fun to me. It screams vanity and boredom. I have been with both kinds of guys and I find the in-shape, but not over-shaped guys are the best.
If you care about your body, by simply eating healthy and running, then you should look good. Not like the bulging man from the bo-flex ads, but good.
Large muscles are overrated. Just be healthy.