1. I usually prefer small gardens. Big gardens are usually too hard to make look pretty. But this garden? This is an attractive big garden. - In other words, of the set of "big gardens" this one is attrative.
2. The garden is both big and attractive. Some may put a comma after big: This is a big, attractive garden.
Well, I looked up the order of adjectives, and it says that judgement (attractive) should come before size (big or small).
But "attractive big garden" just sounds like the wrong order to me if you simply want to say the garden is both big and attractive. It sounds instead like you are giving your opinion of this garden with the category of "big gardens." Likewise with small. Apparenly my