You look like youve got the same body type as me ( or what I use to be like)
Low body fat , super speedy metabalism , its awesome.
Focus on gaining size ( eating shit loads of carbs and protien)
Doesnt matter if your Bmi goes up a little bit when your gaining size because if your anything like me you will loose it in a matter of weeks and tone up quite fast
Follow a rigid workout routine 100% effort every day or dont bother at all
Typical hypertrophy (What you wnat to be starting off on )
(Look into strength training 3 months in and alternate between hyper trophy and strength)
Tuesday - Chest and Tries ( everyone starts on a monday less competition for chest equipment on a tuesday and you can get max effort out)
Wed - Legs + Weighted abs ( Important to keep your body in proportion and it releases shit loads of testosteroe and growth hormones)
Thurs - Back and Bi's
Friday - Rest
Sat - Shoulders , delts , wings etc
sun - Abs
Mon - rest
http://www.bodybuilding.com/guides/muscle-building for your basic routines
Its as pretty basic as it gets
You will see a difference and feel a difference within 2 weeks but realisticly your looking at atleast 9 months before your anything like that.
Hope this helps