Well insofar as what to build it really depends on what you have...
If you look like you just escaped from a japanese POW camp then yeah you need to put on abit of muscle mass. On the other hand it you are built kinda like a regular guy then just tone up abit.
There is also the issue of target demographics, if for instance you want to score with intellectual uni chicks then the arnie look is certainly not the go. If you're more interested in skanks then the arnie look is more appropriate.
My advice would be to build up shoulders/upperback (the V-back bubz referred to is largely derived from shoulders/upper back), chest abit as this is an area which provides a good basis for a 'fit' look. Abs sufficient that you have some tone and no gut. Arms sufficient that you can look reasonably impressive but not as big as your head. Chuck in some weighted squats to tone up your legs/arse.
And on top of this as earlier suggested take up a martial art. Its great exercise, tones, you up, keeps you suple, enables you to kick arse and is generally considered less of a wank than the gym. As far as suggestions of a particular martial art capoeira is good.
So I'd say given your aims and my recommendations you need an axercise plan something like the following:
Gym 2 days a week, doing a general work out eg exercise all the relevant muscle groups on both visits.
Cycle at least 10km a week.
Jog about 5km once a week.
Swim (overarm and breastroke) twice a week.
Do a martial art once or twice a week.
Obviously alternate these around so that there is a good gap between the same exercise eg gym on mondays and fridays not on consequetive days.
i like them in between, some muscles are always nice but arnold schwazenegonka definitely doesn't do it for me...!
