Hi, I would like to make angles similar to the pre-preg ones on sale on the EC website, but in epoxy + fiberglass.
Thickness has to  be 5mm.
What is the best way to build the mould?

Just to add...you'll probably get a better 'ready-made' mould tool using polished stainless steel angle. Most aluminium doesn't have that polished finish and can often have small scratches that will transfer to your part