[southeastflorida]

cedar seems too soft
painted plywood is flat but synthetic, might have chemical smells
pine might warp with those wide dimensions.
cypress ?

 

[fish_stix]

Cedar works fine, but expensive.
Plywood works fine, and is cheap, so used by thousands.
Pine is used by 99% of equipment manufacturers, works fine.
Cypress is used by a few, expensive, works fine.

!st Rule of Beekeeping: the bees don't care; they originally, and still do, lived in rock crevasses, trees, underground, and wherever strikes their fancy.