The saw guide

The saw guide can be made out of just about any kind of 1/4" or 3/8" material like plywood, masonite, flake board, or whatever.
You might be able to find something laying around the shop for free!

The sawguide only has two components, we'll call them the guide ripper, and the sawguide base.

If you don't have a table saw you might seek out one you can borrow for fabricating these parts because if the guide ripper isn't straight as an arrow none of your future cuts with your sawguide will be either.

The guide ripper should be 4" wide or a little more. The sawguide base should be the entire width of the saw foot base of your circular saw, plus the four inches for the guide ripper.

Both the guide ripper and the sawguide base should be about 50 inches long or enough to lap over the width of a 4 by 8 sheet of material.