func_bomb_target and func_buyzone are entities. Do you remember that in the tutorial superjer explains how to use the lightbulb button? Those are point-entities -- they do their job in only one spot, or everywhere.
The entities I mentioned are brush-based entities. This means you make a brush and tie it to the entity. Brush-based entities do their job in the space of the brush they are tied to.
Now that you know, you can follow the instructions in my last post.