pros and cons of a three level critter nation

I've been thinking about getting the add on unit, I'm just wondering about the pros and cons that could come with it. reason being is I have an aggressive lone rat who attacks my others in one level and five in the other level, I would love to be able to give them the whole cage. If I got the third it would be like they do have the whole cage sense they would have two levels.

I was also thinking about getting her a smaller separate cage for my lone girl instead but would want one that is still big enough for at least two or three rats so she still has lots of space.

Please feel free to give me links to other cages as well as your opinions on the add on and cage ideas.

Thanks in advance.

I would suggest a second double CN or a single CN
In a single CN she could be close to the others but out of reach ... so she might get used to them
.... some people have triple CNs but if you keep it off the floor so the bottom doesn't get drafts, it is very high

Hope you do not give up on intros .... I have had rats that were very difficult to intro, one boy even tried to kill other rats,
but they all eventually found rattie friends (http://www.ratshackforum.com/forum/showthread.php?t=32368)

She can not be introduced to them, she had other cage mates but they have past, I had tried intros with the other rats, when she had cage mates and she would not accept them.

She attacks them and is almost three, one of them got a big bite on the side of the face, and she has got her side before, the others have had multiple tail bites from her.

She seems happier on her own.

I have 3 triples and i have two of them broke down into 2 sections for one group and the bottom for another group. It is tall and harder to clean I am 5'9'' so use a small step stool but I love my triples. I left them on the legs and not on the floor alone because they get to much crap all around there. I wanted to be able to clean under them.

I have considered changing my set up to a triple CN, but it would be such a PITA to have to drag a step stool around to access it, and when somebody decided to climb up and hide behind the third level it would be practically impossible to retrieve them.
When I had my two older girls and they didn't want to intro, I kept them in a single CN next to the DCN. It is a nice sized cage. When I am not using it, it breaks down pretty flat for storage. I also have a back up cage, a Living World Rat Resort. It is smaller and has a crappy little door, but is handy when I rescue one or two rats and need a temporary cage.

I have a triple and love it. Yes it's tall but I don't find it hard to clean. I am 5'2" and just keep a two-step step stool beside the cage. They have so much room. But if you have the width you could attach them side by side instead. You can attach a single critter nation onto a double. There just won't be any opening for the ladder. Either cut one or put your lone girl up there and they can't get at each other. You also have the option to take it off later, then.