Network Hearder to be craeted at Top WBS only

Hello All,

Please guide me in creating proj structure, as I am new to SAP PS.

My requirment is I want to create project structure like there will be only one WBS at level 1 (L1), and under this will have various WBS at level 1(L2). Now under each L2 level WBS i need to create activities. But the prob is the movement I create activity the system create Network Header on its own in background.

Already in OPSA i have set (Network asst : 1 For project definition)

My proj structure is required as follows :-

PD :- Office Building (Project definition)

L1 :- Office Building (WBS L1)

NW:- Office Building (Single network at L1 WBS)

L2 :- Civil Work (WBS L2)

L2 :- Mechanical work (WBS L2)

L3 :- Electrical Work (WBS L3)

Please guide me in this regards do I need to do any confic settings or Validation????

Any inputs in these regards will be highly appreciable.

Regards,

Priya