How To Make a Roman Shade -
This site is great and has a "Hardware Calculator" that allows making your own Roman Shades so much simpler. All you need to do is plug in the dimensions you want your finished product to be, answer a few simple questions regarding the shade you desire, and it provides all the necessary information you need to make it. The site also contains instructions, FAQs, and variations of styles to help you prior and also along the way.
Here is one I made using this site and their "Hardware Calculator":
Hope you give it a try!