We have already dismantled he concrete wall along with the RCC Columns. Hence you can use the same centre line and use the available Piles which are already there. You may do pile cappings as you deem fit and have a larger column footings as u desire. If u need u can also drive new piles. Hence you can maintain whatever you planned originally. No need to change the centre line. Only take care while designing the roof truss, purlins and roofing pl ensure that they match with existing roof sheets so that there will be a common Gutter at the centre.