Translation:Who is the developer of that school building?
With the way "developer" is used in English in this sense - that is a large company that buys up real estate, puts buildings on it and sells them on, it's more natural to say "Developer FOR that school building", rather than "OF" when you're talking about a single building at a school.
Now, if "gedung sekolah" is plural, as in the developer is building an entirely new school full of buildings, you might say "OF"after all.
Complicated, I know, and don't ask my why.
Anyway, since this is an Indonesina, not an English course, the only important thing is just to add "Who is the developer for that school building?" as an acceptable response.