...muscle mass?

So I've been lifting weights for well over a 3 years now and I've been happy with my results so far. That said, the problem I have is that I want to be bigger.icon_confused.gif And not "husky" bigger but actually more muscular defined.

I work with pretty heavy weight already and I lift four times a week. What I wanna know is if this is the way to go about building muscular mass. Is there a partucularily effective routine for accomplishing this or is slow and steady the way to go. I'd really appreciate any help!