where can i take a long distance bus to Guangzhou from futian port building in shenzhen.

Well, walk through the border and reach Futian Port Station from Lok Ma Chau. You can take subway Longhua Line to the Conference and Exhibition Center, there transfer to Luobao Line and get off at Zhuzilin. After getting off at exit A, walk southwards to reach Futian Bus Station. (U can also take a taxi to the bus station at the cost of CNY30).

In the bus station you can take bus to Guangzhou directly. BTW, the bus has different terminus in Guangzhou, such as the Provincial Bus Station, Tianhe Bus Station, or Haizhu Bus Station. You can just choose the one nearest to your destination in Guangzhou.