WHAT ICHIGO.M SAID! Its exactly what i did for my Sailor Venus cosplay! Its very simple to pleat. All you have to do is pick up the bit of the fabric you want to pleat at the place you want to pleat it and puch them together in a Z shape and make the Z at the back the length you want to make the pleat in your case an inch. For example
LIKE THIS. I'm a bad explainer. I like pictures.
In the name of the moon, I will punish you!
Will do commissions if anyone is interested...