"I see a bird on the roof."
Translation:Ben çatıda bir kuş görüyorum.
A reasonable guess, thank you! Unfortunately, I did not receive any feedback upon reporting the translation. (When reporting to the Spanish team, I have repeatedly received feedback in the sense of, "Thank you for your proposal, we are now accepting this translation" – they seem to be a more active crew than the current Turkish team.)
Also guessing: I think that 'çatıda' acts like a pronoun here, to form the object 'bird on the roof' as a whole. In the Turkish SOV word order it would be like: I (S) a bird on the roof (O) see (V). I think your version means something like: I'm on the roof, looking at a bird.
I do not know the general rules in order to answer this question.
In the sentence above you should use 'bir' for clarifying you want to say
'a bird'. As 'kuş' is a direct object / accusative here it could also mean 'birds'.
(general direct objects do not take the plural form in Turkish)