You want some nice birch and don't mind spending more? Call Boulter in Massachusetts for their bendy birch:
www.boulterplywood.com
They have 1/8" stuff that actually rolls into a TUBE for shipping.
I used their 1/4", which had to be shipped flat, but it was more rigid. Still, NO problem on any of the bends.
You see, for my order, they ran out of the 1/8" I asked for, so they absorbed these monster shipping charges and shipped me 1/4" instead, flat and sandwiched between two pieces of FLAKEBOARD that I was also able to use for my build.
I used the same 1/4 for ceiling and roof.