The design concept of the cats tower is all-in-one-cage which is narrow for human being, but wide for cats. In the all-in-one-cage, cats can eat, can do exercise, can do excretion and can sleep in the cage.
Those are [1]high curiosity to environment, [2]high mobility and [3]high ability of self decision. The high curiosity to environment brings out high ability to move, and the high mobility brings out high ability of self decision. The curiosity is the path to the mobility, the mobility is the path to the self-decision. The three features are genetically pre-installed within cats, I guessed so.
Cats can't stop learning of environment. The curiosity is expressed as [1]freely exploration, [2]freely research or [3]freely strolling. It looks like action gathering information for keeping their own life.
Baby cats hate small cage. Under the situation of lost mobility, genetically pre-installed 'anxiety' come up within cats' mind. I guessed so. Cats want to always keep the high mobility under any situation. Baby cats genetically hate limitation of their own moves.
Freely exploration is necessary for cat's health, but sometimes human being want to confine cats into narrow area for some reason. Notwithstanding confining cats into narrow area, we have to provide environment to freely-explore in order to keep cat under health. The floor of cat cage must be enough narrow for human being, but must be enough wide for cats also. This is the main issue for designing of the cats cage.
As physical exertion for fighting is necessary for men's health, physical effort for hunting is needed for cat's health. It may be possible to keep normal gene without healthy life, but it may be impossible to evaluate normal gene without healthy life. How can we achieve narrow hunting environment in a narrow cage? In the narrow hunting area, cats have to do spiritual concentrating, exploration and running.One of solutions is a Small Aquarium for hunting exercise.
Many cats owners may put cats under free-range in house, but this cats tower is designed for confining cats in house for some reason. Let us confirm you that the confining is not for punishment for cats, it is for human being's activity.
How long time can we hold cats in a cage? How long time can we put cats in prison? Basically, if there is no uncomfortable problem, cats will never cry. If cats is satisfied, they will never say any mew. When cats sense some uncomfortable matter, cats will throw any sign of "free us now!"
We want to define an idea of "patience limitation time" that is from when cats are imprisoned to when cats start to cry. The "patience limitation time" shows comfortability of the cage.
Generally, the reusability of the cage is important for environmental recycle. High frame reusability is considered at design of this cat tower.
The main frame of the cat tower have to be reused for any other objectives such as an interior for human being. Basically, this cat tower is a kind of louver architecture, so then it is useful as a lighting equipment, an interior or indirect lighting. It can be used as planter for any plant also. In addition to that, it is well-ventilated and well flammable, so then it can be used as crematorium. Any cats cage has lifespan, any cats have lifespan also.
At the middle part of this cat tower, a 300x240x140 sized aquarium is equiped. It is just an aquarium for human being, but it is useful for cats as training of hunting sense. Any cats tend to stare fish in aquarium with their own genetical hunting sence. I guessed that it is well for their brain.
Cats like hemp string as a toy. Hanging something interesting by hemp string from upper part of the cat tower, cats tend to enjoy climbing the cat tower. I guessed that it is well for their brain also.
The main gate of the cat tower can be used as a trap for capturing cats. By moving vertical bar of the gate, the gate will be closed automatically. If you equip this cat tower in your garden instead of your living room, it can be a trap for capturing.

Step 1: Prepare Timber & Lumber

At first, we had to prepare timber & lumber like below.
I choosed Japanese cedar, but any other wood can be substituted.

Base
(600x40x30) 13
(520x40x30) 24
(100x40x30) 22
(20x40x30)   72(6x12)
(40x40x30)   5

Base-Floor
(520x40x30) 3
(85x40x30)   2
(45x40x30)   2
(270x40x30) 2

Base-Roof
(520x40x30) 4

Base-Stair
(100x40x30) 30(5x6)

Base-Gate
(390x40x30) 3
(490x40x30) 5

Tower
(520x40x30) 60(30x2)
(300x40x30) 6(3x2)
(350x40x30) 10(5x2)
(400x40x30) 10(5x2)
(450x40x30) 10(5x2)
(500x40x30) 10(5x2)
(550x40x30) 10(5x2)
(600x40x30) 4(2x2)
(20x40x30)   120(4x30)

Veneer board for Base
350x350   1
520x10    5
520x400   1