Irregular shaped Mesh Creation

All the videos and tutorials I have seen for Kangaroo, they start with a nice, neat, rectangular mesh. The project I am working on is a tent, so I am going to be cutting fabric parts out of a larger piece of material.

So really what I will have are irregularly shaped parts, that are cut out of a rectilinear mesh, how do I model this in grasshopper / rhino to apply to my Kangaroo model?