Here's my guide from my sewing notebook for making the Roman Blind.
DISCLAIMER: I'm not saying this is the correct way to make them but it's the way I make them!
My Roman Blinds were to fit inside the window recess so I just measured from top to the sill and added 1.5cm at the bottom for the seam allowance. At the top I added around 20cm so I had plenty of room for adjustment (see later).
I used lining with interlining already attached. I never use separate interlining any more as I find it too fiddly and you can buy lining with attached interlining for cheaper than buying it separately now.
I cut the interlining to the same size as the fabric, right sides facing and sewed around 3 sides, leaving the top open. After pressing and trimming the seams, turn it the right way around and press again to get a crisp look. Pin all over.
When it comes to the dowel pockets, Ive seen quite a few different ways to do these. I chose to make separate pockets that I sewed on. Also I did not put a dowel inside the blind or sew the ends of the pockets once the dowels were inside the pockets because I wanted to be able to remove the dowels and be able to machine wash the blind when needed.
The dowel pockets were made from the lining (cut on the bias) and tacked to the blind before sewing on. I love this Momo fabric but the butterflies were unforgiving of any errors in sewing across. However it did make sewing in a straight line easier :) Hand sew on the little rings onto each pocket around 5cm from the edge and at even intervals. Attach cords and thread them through the little rings.
I put my lowest pocket at around 10cm from the bottom. Then spaced the rest out at around 30cm (depending on the fabric pattern as I didn't want to sew over a butterfly). After the pockets were on I then remeasured the whole blind and folded the top inwards (both fabric and lining so it creates a neat edge), pressed and sewed it shut. When sewing the pockets on you loose some length and your blind will no longer fit, that's why I leave closing the top until last.
I used half sew and half stick velcro. Stuck one half onto the face of the batten and I sewed the other to the blind. An eyelet is screwed into the batten at the same place as where each of the cords are and an additional one at the end on the side where you are going to tie it off.
Then hang and wait for the dark so you can drop them down!
My Blue Momo blinds are for my living room so I used quite thin interlining as I needed them only for privacy and not to block out light but you can also buy blackout lining if needed.
For a bedroom I used Erin McMorris Wildwood for curtains....
& again Erin McMorris to jazz up an old duvet set. I dyed the duvet grey and made these easy pillowcases.....
.....which when I get tired of them I can cut up and make into something else :)