I made the 'cinema dress' earlier this year and purchased the stated amount of fabric. Surprisingly I didn't have to add anything to the length of the pattern, I'm about 6'tall, and still had sufficient fabric remaining to sew a short straight skirt for DD.
If you're shorter than me I'd suggest that you check the measurements of the pattern pieces and try a layout of your own as you'll probably get away with using rather less fabric (and save £ too)