It kind of depends on the pattern your friend picks for the squares. How loosely it is crocheted/if there are bobbles or other details that may eat up yarn/etc. Granny squares can be almost any size - 4,6,8,12 or whatever inches. I don't think there is a particular 'standard.'

You should be able to figure out how much yarn to buy if she makes one square to start. If my math is right, a 93*93 inch spread would require about 240 6 inch granny squares. So how ever many yards of yarn the square took, multiply that by 240 to get your total yardage and divide by the number of yards per skein.

If you try and figure all of that out before she makes a sample square, you run the risk of getting way too much yarn or not having enough and not being able to find more in the same color.

Good luck. I think the orange sounds cool.

Here is a link that might be useful: craftfetish blog

Thank-you very much!

Curious, since, if its going to be monochrome, would you consider any other pattern possibilities? Only thinking, putting together an entire bedspread of one color units will at some point bore them silly . . .