Well, necro post but timely none the less. I just made myself one of these a few days ago.
Its pretty easy, if you got the right tools. What isn't, right? This is a project that is gonna need a walking foot industrial machine I'm afraid. Ok, you might be able to do it with a home machine if it can maintain bottom thread tension but if your gramma's old singer can't do it, you won't be able to either. The build ups aren't too big, but that 1/4" closed cell foam thats padding it is gonna seriously cramp the style of all but the most beefy of 1950's all steel machines.
Here's a look at the backside:
I made mine to fit my Athlon Argos BTR and Ruger American Predator, so these measurements will vary. I started with 2 pieces of 1000d. Decided to get fancy and do a binding-less build, so instead of using edge binding, I sewed the pieces together inside out along 3 sides and then reversed, sewed a seam along those 3 sides again to flatten it, then put the 1/4" foam inside. That was a pain. Sticky coating on the fabric and foam just don't play well together. No sliding anyway. Then I closed the 4th side. With me so far?
I took a 2" strip of 17337 coyote tan webbing and made a handle out of it, then sewed it on. Took some 1" webbing and made some straps with some non fastex buckles I got from a supplier. Fold the end under before you sew it down, that way the webbing doesn't fray and look like your dog or toddler has been chewing on it. Made a couple of flaps to cover the lenses out of 1000d scraps, cut them to sort of fit and put some 1/8" foam in there to give the end some padding. Sewed some hook tape on the flap and some loop tape on the body, then sewed the flap on.
Thats basically it. Easy peasy. I don't have any dimensions really, because I don't keep track of that while I'm busy copying other peoples work. I didn't take any construction pics cause I didn't think of it. Maybe if there's interest I might make some tutorials.
PS: Copying someones design for your own use is cool and all. I do it mainly because I'm broke as shit and I've got sewing machines and fabric and webbing and all that crap coming out of my ears. If I need a thing that I can make, I will make it. Having said that, don't go copying someones design and selling it. That is low. Design your own if you want to get into the sewing biz.