Help on on new humidor cabinet build

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I have a friend who is a cabinet maker here in the UK and he is interested in building a cabinet humidor, potentially to see if its something he could start as his semi retirement business taking bespoke orders as we have no real options here.. He knows nothing about humidors as such and has asked for my advice ?. Other then knowing they are Spanish ceder lined that's it. Can anyone point me in the right direction for some basic plans or perhaps a video where someone has made one that can give him some clues. We are looking at some form of active humidification but not temperature controlled.

Thanks in advance.