Has anyone ever tried rough sawn lumber for hive bodies? I was thinking of building some out of rough sawn cypress, but wasn't sure if the rough surface would work.
I run my rough sawn lumber through a planer just to make it all uniform. I'm sure the bees don't care if the inside isn't smooth. Just be sure the moisture content has stabilized to your area.
Unless you working with quartersawn material or one of the cedars it is pretty unusual to find a dry rough sawn board that has not cupped at least 1/16-1/8" often more depending on width. There are tricks for flattening or using cupped boards and keeping the rough sawn surface, but really it is far easier to at least partially plane them to flat and even thickness before trying to do any joinery if you want tight consistent work.
there are however folks out there who believe that a roughsawn surface encourages greater amounts of propolis, and that this benefits the hive. It would seem better to me to true the boards and then scarify/abrade the insides if that is your goal.
The inside of a rotten hole in a tree certainly isn't smooth. For that matter it isn't straight either. It's more round or unevenly shaped. You should be fine.
Sam Comfort (anarchyapiaries.org) uses rough-cut wood for most of his many top bar hives.
The bees don't mind at all.
:)