In the Builder, each Room that you create will also contain each System that you create. The logic here is that you can create a Room with Audio and Video Systems, then create another room and you will automatically have empty Audio and Video Systems ready to be populated for that room. Rooms and Systems essentially work as filters, or tags assigned to gear.
NOTE: If a System does not have any items in it, it will not show up in the final proposal. You do not need to worry about having empty systems in the builder.