IDOC segment

Hi frds,

I don't know much about IDOC.My task is as follows

"

The text message is to be populated in a newly created header IDOC segment that is at least 200 characters.

Message text field and the new IDOC segment must be of the same length of 200 characters

"

Can anyone please tell me how to proceed in this,

Thanx in advance.

Regards,

khushy