I made mine from some seasoned oak (cut tree in my garden, let wood dryout well then drilled holes. ) but make thick walls cos I bought some which looked grat and less chunky than mine but after a year or two the fish had chewed the side out.
guess you can drill holes on big piece of bogwood.
I bought some bamboo and slate ones on ebay, fish loved them but after 6 months the bamboo rotted.