The dumbbell is a primary tool of strength training and therefore a primary purchase when you want to build a gym. In my opinion, this is where you should invest the most money. And the only brand I recommend is Watson.
Charles PoliquinWorld Leading Strength Sensei
Watson has by far the most innovative and well designed line of training bars anywhere in the world. The designs are outstanding for maximising muscular development, as well as adding strategic variety to your training regiment.