I have seen a few things about how to make a bee hive escape board, but never any plans. This article includes a dimensional plan and a description of the details not included.
Download the Plans [PDF]
When you are ready to assemble the triangle, cut 3/8″ spaces for each of the 3 corners. This will give you something to align with as you push the parts together.
Hardware Cloth:
https://amzn.to/3EebZU5