By the end of next July this building----

因为这里是将来完成时态.
by the end of +过去的时间,句子一般采用过去完成时
eg:we had planted more than 500 trees by the end of last month.
by the end of +将来的时间,句子一般采用将来完成时
eg:i will have finished reading the book by the end of next month.