Design Sizing

Hi! I am creating digital scrapbook layouts in Photoshop and eventually will order a 10x10 book. I want to know what size I should create my layouts in so that when I eventually order my book it's super easy. Should I design & save my jpegs in 10.25x10.25 or 12.25x12.25? I have read multiple comment threads and I see that either way is an option, so I guess I'm wondering which is best and will eliminate troubles when I order. Thanks!