Getting information in MS SharePoint workflow from SAP

There are many tools which offer this function for SharePoint. Try using BCS Business Connectivity Service and LINQ to get data from SAP to SharePoint list and then use that data in workflow.

To write your own custom workflow, you can check this link:

Custom Activity Workflow for implementing Item Level Security in SharePoint Designer 2007

Workflow Link

To create a Visual Studio 2008 Workflow Activity Library project, you need to follow below steps:

• First is to open Visual Studio 2008.
• Navigate to File menu, point to New, and then click Project.
• Next step is to navigate under the Workflow Project Type and select the Workflow Activity Library project template.
• In the Name box, type SendMailWithAttachmentActivity, and then click OK.
• Rename Activity1 to SendMailWithAttachmentActivity.