The largest size in a single dimension I could find is 50cm, which won’t be enough diameter for a 55mm wheel, you could always make two halves from (50x100cm) and then tape them with two seams (I plan on a cone with just the one seam, sealed with Gorrilla tape). I will remove just enough central hole to be a tight fit on the hub, tape drive side internally to spokes, and rim, and tape NDS to just the rim.

There is a site on ebay that will sell you ready cut covers for about £30, which might be more cost effective.

EDIT: And the single biggest change in my position to much more aero has come from fitting a forward (actually a reversed Thomson layback) seatpost and shorter saddle. This rotated me forward to a position not attainable on a road bike with typical geometry.

That’s exactly that I use.

This was a few years ago mind. I now have a 130mm adjustable stem that allows me to get lower, and I also rebuild the wheels with deeper rims.

Looks like 1mm or .8mm ABS sheets can be used. They come in 1.3 x .66m sheets.

http://forum.slowtwitch.com/forum/Slowtwitch_Forums_C1/Triathlon_Forum_F1/The_ultimate_DIY_disc_wheel_cover_how-to_thread._P3552095/

I might yet go to ABS, I’m pleased with the initial results and have tested them on the turbo at excessive speeds. A club mate has raised concerns about the structural strength of taping (which I have now tested on a rig), so I’m treading carefully at the moment with regards to field testing.