Fixed price projects costing and billing in Projects

 Hi Folks,

Could some one explain me the mapping of Fixed cost projects in Oracle Projects module.

i.e how system will capture project cost by resource, how they will intimate to Payroll to reduce the cost from payroll i.e if i haven't adjust this cost  my employee liabaility will show as  double when transfer to GL. so we want to create adjustment entry in payroll as well to reduce payroll .

And my billing is based on Task (Oracle Implementation is based on Multiple stages i.e BP 80 sign off, UAT sign off, project sign off) since we need to define detail tasks in Projects creation time i.e (Initiation is parent task, under this we need to define multiple sub tasks, where as no billing in this phase) completion, in this case how we can define billing cycle based on task completion.