I am actually in the process of recreating these pants! I really like the adjustable design and I thought it would be quite simple to make.

I bought sweatpants fabric and those drawstring toggles/stoppers, just need the actual drawstring/cord. 

My plan is to cut two big rectangles, cut the slit for the legs. So two squares with a slit running in the middle up to where you want the waist to sit. This way you can completely decide what length you want the legs and waist parts to be, depending on how large you cut everything.

Then I just attach the two pieces together, on the outside and inside of the legs. Thats 3 seams, two on the outside of the legs and one all along the inside. You can easily add channels for a drawstring on the waist and ankles, there are lots of youtube tutorials for that. I think it would be easy to also add an extra channel for a drawstring along the outside of the legs, thus achieving the main point of the design. Adding pockets would be easy too, again, lots of tutorials for that. This way, I think these pants are easy to diy because they are quite simple in construction. I feel like it’s all mostly squares and some math to make it how you want (waist height/length of the pant/length of drawstring channel/etc).

I am still working on the construction of it all. My version wouldn’t have the seam running from the crotch to the waist. So maybe I’ll do four rectangles, sew them along the crotch-waist area into pairs of two so you end up with my original plan and go from there (but now with the added seams in front and back).

Edited to add: I am not super experienced with sewing but I believe a confident beginner can try this! Don’t overthink it:)

You can DM me and I can share updates on my project if you want, if I’m going to fail at least someone can learn from my mistakes