Basically it seemed to me like the only Oozaru capable of fighting was Vegeta. And this is because he maintained his consciousness. The other Oozaru's were just rampaging, shooting off all their power, and destroying everything around them. They weren't really trying to protect themselves at all. Even Goku against Roshi, Oozaru Goku wasn't trying to fight Roshi, he was trying to destroy EVERYTHING, lol.
I think that the Oozaru's probably can't control their ki very well, if at all, without training. That might have been why Goku never used any Chou Makouhou blasts as a child Oozaru.
Anyway, Roshi seemed pretty confident that he could have taken Goku out. And who knows, maybe he could have buffed himself enough with Max power form, and with charging his kamehameha to actually do so. But the only PL we've seen from him is 139, and he was supposedly a 180 against Kid Goku. If that's true, then there's absolutely no way that Roshi could have done anything to Oozaru kid Goku, unless he somehow knew Kaioken or something. That's just way too big of a gap in power levels. Even without paying attention to Roshi, Goku's sheer durability would tank the blast like it was nothing. Which is crazy, given that it was a moon busting attack.