Some think it was a Scribal error - the word gopher, for which there's no translation (hence they don't know what type of wood it was) could actually have been kopher - which means pitched wood
ie wood treated with pitch!
My own guess as to what type of wood it was would possibly be cedar because it was plentiful in that region but if my theory above is wrong then it could have been gophar wood - ie cypress.
Edit - actually I'm sticking with cedar as apparently it is rot resistant!
Bloomin scribes messin' wit' vowels!
So what do I win???