I haven't come across Fiberglass mesh for baking buy if it is sturdy sound like it would be ok.
If the holes are smaller there would need to be a lot of them so to allow proper air flow.
Having a sturdy material to build it with is important as you need to make sure the body doesn't flex or deform, as it will be packed with carbon granules.
Any flexing/deformation may mean the carbon doesn't stay correctly packed which could mean improper air scrubbing.
Preforated metal sheet can be easily found on ebay.
For everyday grows in 3' x 3' spaces etc, I just buy off the shelf, for more specialized spaces where buying off the shelf isn't an option, this is when I would build a filter.