Making a costume from a bed sheet

[ineedacupoftea]

We're going to see the Rocky Horror Show in December and I really don't fancy paying lots for a costume that will be worn once, so I was thinking about making an operating gown (like Frank n Furter wears) from a bed sheet.
I do have a sewing machine and have made a child sized dress before, but I'm clueless where to start with this - any hints and tips would be very welcome!

[Fatmomma99]

as long as you wear stockings underneath, all will be well!