The Garden of Evening Mists by Tan Twan Eng (2012). A Malaysian novel set partly in China, this isn't specifically about Suzhou but its exploration of Chinese garden design philosophy — particularly the concept of creating landscapes in miniature — is one of the best literary treatments of what Chinese classical gardens are trying to do. Read it before visiting the gardens and the experience changes.
Soul Mountain by Gao Xingjian (1990). The Nobel Prize-winning novel follows a solo journey through rural China in the 1980s, including time in the Yangtze Delta region. Less a narrative than a meditation on Chinese cultural identity, it gives a sense of the literary and philosophical traditions that produced the scholar-gardens of Suzhou.
Oracle Bones by Peter Hessler (2006). Hessler's account of China in the 1990s and early 2000s is the best-written of the many foreign-reporter books about modern China. He spends time in the Yangtze Delta cities, and his descriptions of the collision between ancient China and rapid modernisation illuminate what you're seeing in a city like Suzhou, where a thousand-year-old garden sits next to a new tech park.
The Silk Road by Peter Frankopan (2015). Suzhou was the source of much of the silk that travelled westward along the trade routes to Rome and beyond. Frankopan's history of the Silk Road explains the economic and cultural significance of Suzhou's silk industry in the wider context of ancient global trade.