Thanks bearisgray. I think I will go with a nine inch block, that seems to be the over riding opinion from everyone!
I already figured out the measurements and how many blocks etc. I did a spot of accounting last year in my old job, so it was a nice little mental exercise to figure it out. I've even figured out how much fabric I'll need, I'm quite proud of myself.
Thanks everyone for you advice, it's really helped. Of course I will post pics as I work on it, but don't hold you're breath as I have to finish my current project and save some money to by the fabric for it!
Thanks again everyone who gave advice!