I've started building myself a Dan Leigh R8 delta from the plans on Dan's site. But I found it quite a challenge to work with the large, slippery sheets of ripstop. (My table isn't large enough to lay the pieces out flat.)
At the cutting stage, I needed to double up the fabric and cut both halves of the sail together. And I was pretty sure I'd mess this up if I tried it while things shifted uncontrollably on my work surface. So, instead, I tried hanging the whole thing on the wall and it made cutting quite easy!
I hung the fabric, doubled over, on a piece of aluminum bar, held to the wall with masking tape and tacks. Then I added some tacks near the lines I needed to cut (on the scrap side). Cutting was easy, starting from the bottom and working my way up. The fabric stayed flat and the two halves stayed together.
I definitely recommend this approach if you find yourself trying to cut ripstop with some precision.