Upgradation from SAP Business One 2007 B to SAP Business One 8.8

Hi.. Guys

currently we are implementing SAP Business one 2007 B and we need some functionality to be customized as per our specific requirement. Also we are planning to upgrade from SAP Business one 2007 to SAP Business One 8.8.

Right now implementation is on going. please let me know whether we should upgrade before customization or we can go for upgrade after cusmization ?

please give me the clear picture.

Regards

Rakhi