We've made arcs using curves of corrugated too John - the metal works fine but the wood, so far, has been a nightmare
We used 12mm exterior ply first time round and it lasted a matter of months (got to stress it was fully grown, Large Black & OSB sows & a boar that were housed in them
) we then upped the thickness to 18mm exterior ply, it lasted a bit longer..............but not much
I suspect for a long lasting (adult proof) arc you'd need marine ply - but it could just be a combination of badly behaved pigs and very wet Scottish weather that's been my downfall
We make our floors using pallets, topped with ply/osb board, then covered with stable matting to protect the wood underneath and give a non slip surface