Organisation struture

Hi,

In my organisation Org structure is not maintain properly.

I mean in Org structure we have position, org unit (department), person. but they are not maintain prpoerly Their hierarchy structure is not ,maintain properly , now my organisation planning  to implement  ESS and for that we required proper Org str . we have to maintain this structure in the existing org structure.

Can anyone guide what precaution should we take while changing the org structure .

we have ard 8000 employee in all

Regards

Nutan