I have actually attempted making two fusuits in the past, one with the plastic canvas method, and one with the foam and ski-mask method. I highly recommend the later.
The plastic canvas base has a lot of risk of either not being properly measured in the first place, or slowly warping as you work to where it doesn't fit properly or becomes uncomfortable. Plus, getting it to hold its shape well can sometimes lead too a lot of excess weight that can lead the plastic canvass to break.
My recommendation is to go with the ski-mask+foam. It's extremely light weight, easy to wear, and if you build it around an accurate representation of your head (Or like in my case, I just used my own head) it will also fit very well and not move around on your head like the canvas might.
https://www.youtube.com/watch?v=O73FgEWG2Jk This is the tutorial I based mine of of