The roof doesn't need to be higher than the rear wing as of last year, but if you pass rule 16.5.1 it's almost impossible to have the wing higher than the roof anyway.
16.5.1 Touring Car Body Dimensions: Overall Wing size Inc endplates (WxDxH) 190x40x20Max (mm) Wings (excluding endplates) are to be of single moulded construction (no flat-packs/bend your own) and to be mounted directly to the body (no spacer between shell and wing), on the mounts provided at the back of the shell. All features (front splitter / bumpers) from the original moulding must remain on the shell.