regarding requirement gathering

i need few inputs regarding report development

i have one flatfile report format..i want to develop it in SAP BI system.?

so what r the things i need to know from user before going to develop it?

please give me few points which i need to ask the user..wt information generally we need to know before developing the report.....

They given sample report but no spec given .

please advise u r views.

Thx in advance.