Hi Anna
Are there any SAP Standard Web Services you can utilise first?
Check out the this link: http://wiki.scn.sap.com/wiki/display/ESpackages/enterprise+SOA
Also there is a wizard for developing your own Web Services...have you tried making use of this?
Finally, I love using Function Modules remote enabled into Web Services. I find them so quick to develop and all developers can pick them up and run with them.
BOL would be great as new technology, but you'd possibly need to through a Function Module in front of it anyway to manage the initial inputs, (forum can correct me if I'm wrong)
Good Luck
Regards
Arden