This is basically a test. I've been reading up a bit, and people seem to get kind of testy on this particular board. So. Here's a totally irrelevant question that I don't need to know the answer to yet: when can an Eagle Shaman turn into a roc, and who else can?
Wild Shape (Su): At 6th level, an eagle shaman's wild shape ability functions at her druid level - 2. If she takes on the form of an eagle or roc, she instead uses her druid level + 2.
However, the Bestiary p.236 states that a Roc is a Gargantuan animal, while the CRB p.51 doesn't say anything about Wild Shape allowing anything so big. Forgive me if I don't use these terms correctly, since I'm new; but I think what I'm saying is that the RAW is nonsensical, so I'm asking for the most commonsensical RAI, not a houserule.
What I would say is that the Eagle Shaman can in fact turn into a roc, which is the functional equivalent of beast shape IV (if that spell granted gargantuan animals, which it doesn't). That would put it at 10th level normally -- if anyone else could do it, but they can't -- and so an Eagle Shaman can turn into a roc at 8th (but no other druid ever). What would you say?
I know its daft, but frankly the rules governing Beastshape don't give you access to the Roc because of exactly what you said. BSIV doen't allow for size G. I would throw you the a Young templated Roc as a concession though.
Aha! A truly clever way to resolve the RAW. But if I may extend my test, if you were not as clever as Shifty (and I'm not), then what would you do: say "No roc for you!" </Seinfeld>, or extrapolate size progression on beast shape (but only for an Eagle Shaman) like I did, or... ?
(...)if you were not as clever as Shifty (and I'm not), then what would you do: say (...)
I'd say, put down your PF books and go watch football.
No seriously, the first rule of any RPG is "think for yourself and use the rules to support your game, not to dominate it, if rules seem to be inappropriate in a situation, screw them". There are much to many people who seem to rely on rules that badly, as if their characters would not breath if there's no rule for it. So if it says Roc, you can transform into a Roc somehow. Do something that's not that broken (like Shifty's Young templated Roc) and you're good.