'up on the roof' makes more sense to me in English and, is what I'd expect was wanted if I see the re/ra ending. Any reason it wouldn't be right?
I actually think "look up at the roof" sounds more natural, even though it doesn't strictly make sense. "on" should work too, though. I'm trying to think of when you'd use one vs. the other...
But the current sentence needs to go - "look up to" is a fixed phrase in English that means something quite different (to trust, to show respect for, etc.)
I think (and I'm seriously splitting hairs at this point) that if I say up 'at' the roof, I'd be looking at the roof itself but, I'd us up 'on' the roof if I'm looking with the expectation of seeing something on the surface (a cat, a lost ball or whatever). But. I agree, 'to' is all kinds of wrong
I've never heard about a person "looking up on" something. Climbing on, jumping on, yes, but not looking on. ("Look on" means something totally different - it means to observe the activity of others.) I agree that "look up AT the roof" is the best translation.
I'd think if someone said "he was looking up on the roof" that the boy was looking while standing ON the roof.
If he's on the ground, or anywhere lower than the roof, and looking up, then I would say he's looking up at the roof. Hungarian might use the "onto" suffix, but we don't need to translate that literally. You can throw a ball up onto the roof, but generally, we don't look up onto things. :)
Lots of comments here. The boy looks up onto the roof wasn't accepted but it should have been. There's no magic formula whereby one version is right and all others are wrong. There are some which will obviously be wrong but at the roof or onto the roof should both be fine.