Pre Preg heated in an oven activates the resins and its catalyst.
vacuum Bagging pulls out the bubbles .

the making of a negative mold and Pushing the air-bubbles out with a Bladder inside is the reverse.
the Mold is your Outer surface of the finish product.

Americas Cup Catamaran race Hulls are made in molds , I expect.

Dragon Plate sells carbon fiber tube in all sorts of sizes and shapes and sheet.
https://dragonplate.com/ If you want to Bypass the roll Your Own and go to step 2+.