Unless you have rotated your cabana on either the x or z axis, then the up direction will be the same as the world direction. Transform.up will give you the world space Vector so if Transform.up is Vector3(0,1, 0) and you use Transform.TransformDirection, you will still get Vector3.up. So the number you are reading is correct. And yes, that number is in world space.

I don't think you understand the idea of a direction. Vector3's can be confusing when you first start because they are used for multiple things with different meanings.

1. They can be used for a position. In this case they will be something like your comment (1440, 35, 511).

2. They can represent eulerRotations. That is fairly simple to understand. You might have (0, 45, 0).

3. You can use Vector3's to store Direction. In this case you will get a normalized Vector that is centered at the origin. If you drew an arrow out from the origin through the point, you would get a direction. Hence they are called Vectors. So transform.up creates a Vector3 pointing in the same direction as the local y-axis of the object. If you call transform.forward, you will get something like (0, 0, 1) if your object has no rotation.

Unity makes no differential among the 3. Each function that takes a Vector3 self determines how it uses it. Some might take a Vector3 and use it as a position like transform.position while others take a direction such as Rigidbody.AddForce(). If you wanted to, you could take a Vector3 that was created with a certain use in mind and plug it into a different form.