Hi, I own a costume company and have been using Blender for 2 years now to fabricate props and costume shapes. It’s pretty easy once you get used to it. Model your object, using low poly topology, keeping in mind to model your face loops where you think the real world sheets of material will be used. In other words, construct the object the way you think it should be fabricated using your sheet material. Be sure that each face loop is only 1 face wide. Mark your seams along your predetermined paths. Be sure to apply scale to your object before unwrapping. To be very safe I triangulate faces at this point. Unwrap. Use the Stretch checkbox in the N properties panel of the UV/Image Editor to confirm that it looks unstretched. Export UV map as .eps file (I use a fill strength of 0). Then open the .eps in Illustrator or Inkscape. Here’s the tricky part: Measure one of your model’s longest edges using the Mesh Display/Edge Info: Length menu item in the N properties window, and scale up (or down) all your vector objects in Illustrator/Inkscape program by the correct ratio to make that edge the right length. Overall, make sure you know which piece is which (maybe by labelling) and which way to orient it. Then nest the pieces to minimize print size, and tile the print job onto regular paper or send to a large format print shop for your patterns.
This has worked flawlessly for me for about a hundred objects so far. I can even take into account the thickness of my real world material (I work with foams ranging in thickness from 1/4" to 2 1/4") using the Solidify modifier with the Thickness set to my material’s and the Offset set to 0 (since the outside of my foam stretches by the same amount as the inside surface contracts).
Let me know if I can be of any more help, since I’m very enthusiastic about this application of Blender and am always looking for ways to put it to further practical use.