Pillow case dress help please

[moocowmrs]

I would like to make my girls a couple of pillow case dresses I would like to use up some material I have but one is bigger and one smaller than a pillow case iykwim so how do I work out how much fabric to use. Tried looking on Pinterest but just patterns for pillow cases !

Bumping only because I am impatient !

dressagirlaroundtheworld-va.blogspot.co.uk/2012/01/how-to-make-best-dress-ever-tutorial.html

Thank you, what a great set of instructions. Will get cracking with it tomorrow.