Create a statue, change it into an animal, you mean?
Ah, yes, I had missed the base 25 which my downloaded guidelines list as "Radically change an animal into an unnatural way (give an horse wings)", so I agree with you, this is even harder than what I would have thought, without even considering the metal part.
So yes, for the moment, just doing a bigger horse would do, with the spell Isen proposed to get it to accept a gifted rider.
But why not go the other way and create the metal horse? Especially with the (IMO quite good) HR about specific spells to avoid finesse rolls.
This would look like this (Serf's Parma, so I'll very probably commit errors and omit things, thus final spell would be higher):
First, a ritual:
CrTe 25: Create the Winged Horse.
CrTe base 5, create 1 cubic foot of Iron.
- 2 Mag for 100 cubic feet. Dunno if it's ok. I'm tired and a little lost on anglo-saxon mesures right now, so this could be higher.
- 1 touch
- 0 momentary
- 1 so that this only creates a Metal Horse, but no Finesse roll is needed.
Then Re(Mu)Te: Animate the Metal Horse 25? 35?
ReTe base 3 (control/move in a very unnatural fashion). This allows the horse to fly and, combined with Muto, the limbs to move, wings to flap and so on
- 2 to affect metal
Do we need magnitudes for size? I can't remember. Check hermetic projects, the flying castle, to see if we do. - 1 touch
- 2 Sun
- 1 Muto requisite: Combined with the Rego requisite, this gives the horse the semblance of life, by allowing its wings to flap, head to move a little, legs to stir.. the Muto requisite ensuring that the metal bends, but does not break.
The second effect could be enchanted in an item, or even in a horse, foregoing the +1 touch, bringing base level down to level 20.
Stupidly, again, posting instead of working, I'm gonna regret this... Reading is mostly ok when I can do other things. Posting only postpones work T-T