Frequently there is discussion about upper/top hive entrances and their benefits on this forum (and now detailed in Michael Bush’s book on page 329). Last summer I converted my nine hives to upper entrances and finally had a decent honey harvest from my older hives.
I built upper entrances with a landing board that can quickly be placed between the hive bodies and the supers -- I do not use queen excluders. During the process of coming up with a design I looked at several of Joe Clemens designs (boy do I appreciate his CAD expertise!), the Imirie shim, and in the bee supply catalogs for options. My design is different than most that I have seen. It is constructed from 5 pieces of wood per the attached graphic. I make the opening about 20” in length, slightly longer than the standard 19 7/8” hive box, so that it fits easily on the hive box and there is a crack for a rain gutter on the front edge. As long as the two long shims are cut from good wood the frame is very sturdy.
Contact me if you have questions or need additional information.