[Charley Farley Trelawney]

18'x12' Tom if you can get away with it

You could always say after putting it all together that the shippers made a mistake and have only charged you for the smaller one

Downside of course is she who should be obeyed may feel it has teh room to store/use things other than what you have in mind.

Seriously though, go for as big as you can get away with.

Charley