Your right I’m not using the space! That could work. I haven’t had a problem before as all the buns usually do is sleep in the daytime and when they were younger they both had their own multilevel condo. I have measured and the biggest I could do without rearanging furniture (which I with do if needed) is 3 squares by 4. Height is only an issue for keeping the structure sturdy. They have free reign of the whole flat when I’m in and I used to keep my other buns out at night as thats when they were most active. I got used to sleeping through the noise of scrabbling bunny races! So far my new bunny Koori seems well-behaved but I don’t think shes sexually mature yet so I’m sure there will be naughtiness ahead which is why I am planning on keeping them caged until she proves she can be trusted! With a pen attached I won’t feel guilty at being caught up at work as well!
Thank you for the pics Petzy they are very helpful. Mine will also be a new bond (positive thinking even though their not bonded yet!) and was thinking of small shelves to fit one bunny so that Mizu and Umi can lie and sleep away from Koori if she’s being too hyper for them. They spend most of the time sleeping!

Ok hows about 3 floors of 2×4 and 1 floor or 2 floors of 2×2. The first level will be clear with litter tray, food ect. Second floor is half shelf (2 square by 2 square). Third floor is also half shelf on the opposite side. Fourth floor is L shaped with one square free to jump up. Possible fifth floor would be the same as fourth just with a different place to jump up. Every shelf would be supported by dowel rods and probably be carpeted as they are all litter trained and don’t eat carpet. This would be the set up when they were bonded with xpen attached.
Would it be ok to make it like this now and give Koori floors 3, 4 and pos 5 and Mizu and Umi floors 1 and 2. The way its planned I could easily block off the way up from 2 to 3.
That gives Mizu and Umi over 58ins by 28ins on the bottom floor to stretch out. They are aprox. 19ins long when they are pretending to be a pancake. (imagine their disgust when disturbed their snooze with the tape measure in my hands!) And they have the second floor which is half the size. Koori is 13ins long and will also have 58ins by 28ins and a little bit of a smaller shelf. To be honest its more room than they have at the moment but at the mo they are out most of the day, taking it in turns. (I’m a teacher on summer hols!)
Sorry if its hard to understand the plan. I have it all drawn out! Remember the plan is for them to be completely free range once Koori is trustworthy. Mizu and Umi were free range before Koori came along!