If you do a little burning test you will be able to figure out which materials are in your fabric. Try it with this fiber burn chart
You always have to take into account that natural fibers will shrink. Don't tell me that you haven't had the experience of the new blouse that came out of your machine a few sizes smaller :-( Too bad! The best way to prevent this from happening is to wash your new fabrics before you start sewing. Just toss it in your machine, tumble it dry if you have one. We have learned to snip of the corners of the fabric so it doesn't fringe at the cutting edge too much. It's not really possible to give percentages on shrinkage. It all depends on the fibers that are in your fabric. We mishandled a piece of hemp starting out with 1.75 meters and it came out 1.60 meters. Just that you know...
All regular patterns are suitable for our fabrics. We learned this great tip in sewingschool: draw your pattern on your tracing paper as usual. Than add seam allowances on your traced paper. Seams need about 1.5 cm. extra, hems about 5 cm. extra. Nów you cut out your pattern and lay it out on your fabric. You can cut the fabric pieces more efficient and economic now. Just cut along the edge of your paper and snip the marks on the way (app. 3 mm.). Wanna bet there's more fabric left over than you expected!
A great tutorial to get that zipper in!