Does anyone know if roof bars used on MkIII will fit on MkIV, as they seem to be flush on the new model. 

I've used pound shop roof bars for years and they've fitted all my cars previously including my mk3 estate which had 'proper' roof rails. Unfortunately the mk4 estate has no proper rails and presumably they are only good for the bespoke type of roof bars

The MK4 are flush rails. Unlikely they'll fit if MK3 was raised.