JohnD, yeh, that's what I mean't. Quite new to the concrete game so still learning the ropes.
Not doing the slab yet, but it'll be about 5.8m x 5.6m - slab will be for cars, will get a C25 mix, and will be indoors (once I've got the walls up).
I just did the trench today which was about 6.1m...