Here the 1920 LDS edition changed the present-tense build to built. This change, however, was not marked in the 1920 committee copy, which suggests that this secondary built is a typo. This whole passage (as a future prediction of Moroni’s) is supposed to be in the present tense. Note, in particular, the present-tense buildeth in the very next clause: “for it cometh to pass that whoso buildeth it up …” (Ether 8:25). Perhaps the secondary past-tense built was influenced by the pastparticipial built that occurs later on in verse 25: “for it is built up by the devil”, even though that passive clause is in the present tense (“it is built up”). In any event, here in Ether 8:24 the critical text will restore the original present-tense build, the reading of the earliest text.
Summary: Restore the original present-tense build in Ether 8:24 since we expect the present tense throughout this passage, as exemplified by the present-tense buildeth in the following verse.