guest books and photo guest books

What size was your guest book? I really want to do a photo guest book and have ppl sign that with our pics, but what size do I do? Shutterfly is having a sale until TOMORROW on 8x8 hardcover books. but they only come with 20 pages and extra pages are $1 each... I'm having 220 guests or so... and even though they won't ALL sign it, I can't decide how big to make it!!!

Please help... TIA

I had an 8x8 photobook - honestly like 15 people signed it, but a bunch of people told me that they looked through it