I would say that the sentences follow the S-V-O pattern because they are allowed to, and the author may have wanted to use the same word order as in English. This would also explain the unnatural inclusion of the personal pronoun 'Én.'
However, S-V-O is still the natural word order to a generic question like "What are you doing?" because you want to emphasize the verb in your answer. You would only start your sentence with 'Én' if you want to put emphasis on the fact that you are the one who's watching them.
- Mit csinálsz? = "What are you doing?"
- Nézem a nagy épületeket. = "I am looking at the big buildings."
Exactly. And once you want to emphasize something else in your sentence, you start messing with the word order. One example:
"A nagy épületeket nézem" - "It is the big buildings that I am watching."
I don't think there is any specific rule on a stricter word order in definite conjugation. Or if there is, it is not at all obvious. The word order is very flexible here, too.
Hungarian also makes a difference, but a bit a... different one.
Néz can be translated as "to look at" or "to watch", in the meaning of "looking with interest". Watching something happen, or watching TV.
And then there's figyel, which can be translated as "to watch" as well, but rather in the "paying attention" sense. Watching children, for instance.
And yes, "I am looking at the big buildings" needs to be accepted here.
Nézem is the definite conjugation form - i.e. i am looking at that specific thing. For more, see: https://en.wikipedia.org/wiki/Hungarian_verbs#Definite_and_indefinite_conjugations