Complex sentence: After several years of purchasing, restoring and selling historic homes, he was able to purchase Mercer House in 1969, after it had stood empty for more than 10 years, its last occupants, the Shriners organization, having used the building as their Alee Temple.
Split into simpler sentences: After several years of purchasing, restoring and selling historic homes, he was able to purchase Mercer House in 1969. The house had stood empty for more than 10 years since its last occupants, the Shriners organization, had used the building as their Alee Temple.