Rational "Crown Board" or "Coverboard"
Not really required... But for completeness sake

This item is identical in size and construction to the "National Crown Board"

Use with rim downwards for bottom bee space or with the rim uppermost if top bee space is required.

The holes shown are to suite the standard porter escape.

this page gives methods of cutting such holes. For normal use a single 33 mm central hole proves to be adequate.

Note 1.
9 mm plywood is specified owing to it's greater rigidity and freedom from warping. This durability outweighs the small cost saving of using thinner material.

Note 2.
9 mm is specified for the thickness of the rim material but commercial supplies are often of 8 mm thickness, using 8 mm is unlikely to cause any problems.

Assemble using a waterproof PVA type glue and 16 mm pins or staples.

If you are using a top bee space system, there is no need for the complication of a rim. Many of those that I used personally were only squares of waterproof ply 460 mm on a side and 9 mm thick. These had a 33 mm diameter central hole and were treated with linseed oil and had the outer margins and outer edge painted with exterior grade enamel paint, which helped to stop absorbtion of water into the grain.