Silnylon is kept on a roll to prevent wrinkles. Ironing has been tried, but fear it will damage the sil coating, or even the nylon.
A piece large enough for the pattern piece is pinned on the pingpong table at the four corners, being careful not to stretch the sil fabric.
The pattern piece, if not already so cut, is cut along where the stitch lines will be. It is placed on the nylon, and weighted so it will not shift. Then a line is traced around its edges onto the nylon.
Then the pattern is removed and another line is traced outside and around the inner line with the seam allowance I want.
Then the the nylon is cut at the outer line. Everyone has their own favorite cutter. After trying every type of gadget, I reverted to well sharpened Fiskar scissors. Personal preference, I guess.
Might have mentioned before, that I pin the silnylon seams before sewing with short straight pins, pinned so that the pinholes will be on or inside the stitch lines, and easy to seal, on the face of the faux flat fell seam (faux, because one side of the seam has no overlap outside the stitch line). I sew slowly, holding the silnylon fabric both in front of and behind the presser foot so that it does not stretch or wrinkle. I pull the pins just before the fabric goes under the foot. If the fabric starts to stretch or wrinkle around the pins, it is time for a long break, and a restart later. Why do I suffer this way?! I suppose a shrink might say it is masochistic, like backpacking. But BPL has greatly improved the latter, and with experience, the sewing gets less tedious. And it is quite satisfying to weather a storm under your own handiwork.