In theory, once the roof is in place, the walls will follow pretty quickly. I'd like to say 1-2 weeks... but this is a self-build and I'm often alone on site so nothing is guaranteed. Having slept on it, I'm inclined to put the walls up first. The winds have been picking up here (we've had 50mph gusts running along the valley in the last few weeks) and another week or two without a roof covering is preferable to having to recover my rafters from the neighbours property and put them all back on the roof.
Thanks for the reply.