The Bible doesn't forbid Christians to construct beautiful churches. In fact, if the Bible is our guide, we should expect Christians to build fine churches to express their faith.
In the Old Testament, God commanded the Jews to build a magnificent Temple in Jerusalem (2 Sm 7:13; 1 Kgs 6-7). In the New Testament, Jesus commended the poor widow for contributing to the Temple's upkeep (Lk 21:2).
The Lord showed his own love for the Temple by driving out the money changers who were desecrating it (Jn 2:1-17). Remember also that Christ rebuked Judas, who complained about using precious oil in Jesus' honor instead of selling it and giving the proceeds to the poor (Jn 12:3-5).