I agree with the gal who said get the measurement of the frame and add at least 6 feet to both the length and width. 8 feet would be even better. You need to get to all 4 sides of the frame. Make sure you get the 'footprint' measurement of the frame, not just the quilting area.
I have a 10' frame with an 18" machine in a 8 X 16 foot space and it just fits.